One thing you might NOT want to plant that is commonly suggested for both hummingbirds and butterflies is Buddleia or Butterfly Bush. It is invasive in many regions of the US and in some states is considered a noxious weed (illegal to sell) - I can't say about Ontario, you might want to check with your equivalent of the local extension agency to find that out.
However, there is a new hybrid cultivar called "Blue Chip Lo & Behold" that is said to be noninvasive that might be appropriate - if you can keep it alive in your area. It sets very few seeds and those may be sterile.
People in Ontario seem to have trouble growing Buddleia as a perennial - if noninvasive in your area, you might be able to treat it as an annual, replanting every year. But it would probably be better to look for local native species instead.
Another plant to avoid is Trumpet vine. Seems like everybody and their brother has trumpet vine on their list of wonderful hummingbird/butterfly plants. It attracts the hummers, it is true - however, it is also extremely invasive, much more so than buddleia. Its even worse than Japonese honeysuckle (another plant to avoid like the plague that it is). I live in the desert and the trumpet vine that my backyard neighbor so thoughtfully planted way up a slope far from his house along my fence continually puts out runners that come up all over my yard - despite the fact that the previous owner had it patio-ed, rocked and astro-turfed in. It comes up through the weed barrier into the rocks around the shed and then tries to grow up the shed walls - and trumpet vine is one of the, if not THE, most damaging climbing vines to house siding on the planet. It has grown 40' across a barren wasteland of astroturf and rock to come up in the middle of the rose bushes in the 3' wide planting bed around the patio.
I know it's hard to tell, but I HATE the stuff.
Also avoid Virginia creeper, which I occasionally see suggested as a hummer feeder plant. I have no idea why. It is nearly as invasive as Trumpet vine, and nowhere near as attractive.
So what CAN you plant? How about some Asclepias? That is Butterfly WEED, instead of Butterfly BUSH (Buddleia). It not only provides flowers for hummers and butterflies, it also provides munchies for Monarch larvae.
Also - Cardinal vine. It is a climber, but not invasive like Trumpet vine. I think it is also called Cardinal Climber. Scarlet runner bean is an excellent choice that will not only feed the hummers and the butterflies, it will feed you as well.
Monarda (Bee Balm, Bergamot), Salvia, Penstemon, Hollyhock, Rose of Sharon, Delphinium, and Aquilegia (Columbine) are all good hummer plants. Fuschia reputedly attracts them as well, but I've had poor luck with the plant myself. I do love Fuschia; but having to replant it every year was sort of depressing. I stick to keeping it in hanging planters these days.
There are several varieties of Hyssop that attract hummers - one is called Hummingbird Mint. Clove pinks and some other dianthus are attractive to hummers. There is actually a rose that is attractive to hummers, I think it is called Candy Oh!
Most of these are widely adaptable and should have varieties that will do well in your area.
Here is a longer list of flowers that are attractive to hummingbirds - hopefully you will find several plants that are hardy in your area:
Thanks very much for all that info! I do have a rose of sharon bush in my yard but haven't noticed any hummers by it. It blooms very late and the past year it had very little flowers.
I've read that the flowers from hosta plants attract hummers, is that true? I have a bunch of them but I have always cut the stems off because the tall stems made the yard look messy. (I'm leaving them this year).
If the Rose of Sharon blooms late, it may be that the hummers just aren't finding it. You will want some early blooming feeder plants to attract hummers - they tend to return to an area once they find food there. What probably happens is that the hummers have already picked out the "best" feeding sites based on early feeding ground finds.
If your Rose of Sharon is putting out small blooms, it may need some attention - pruning, fertilizing, or other soil amendment. Look into the specifics of growing the plant in your area, it may need some TLC.
One way to help attract hummers to your yard while you are working on establishing plantings for them is to put out feeders. There is no harm in doing so. Just use the typical 1:4 mixture - 1 cup of white granulated sugar (NEVER brown sugar, molasses, honey, or turbinado, only WHITE GRANULATED SUGAR) to 4 cups of water. Keep it in the fridge. Fill the feeder (I prefer the Humzinger feeders, that look like flying saucers) and change the nectar out every 2 or 3 days, depending on temperature. I clean the feeder out every time I refill, and run it through the dishwasher about once a week. Hanging the feeders in the shade is good for the nectar (it won't ferment so fast), but in sunlight (if not too hot) is better for the birds. Dappled shade seems a good compromise.
I got a "regular" sized Humzinger at first, but found I was throwing most of the nectar out. It was just too big for the one or two hummingbirds I was getting at my last location (first year for the feeder, moved away in June, so it was only up about 2 months). I replaced it with a Humzinger mini and I find I prefer these a LOT because - hummingbirds being very territorial - you can hang them all around the yard out of sight of each other, thus having many feeding stations and less fighting over them, without having to put up big feeders that waste a lot of nectar. I also have one of the Humzinger window feeders but have not put it up yet.
EDIT: Apparently hummers do like at least some varieties of Hosta. They also will feed from lilies and daylilies. But again, I think hostas tend to be late bloomers - so you want to be sure to present a progression of blooms for the hummers throughout the season. Feeders will help to smooth over any gaps in the progression and will not discourage the hummers from visiting plant sources of nectar.