In Bangkok, Suan Luang and Suan Rotfai are nice places to walk and see birds.
Pattaya town may be sleazy, but the environs are fine so don't be too dissuaded. Bang Phra is certainly worth a visit if you go that way.
Otherwise, consider the Hua Hin direction instead, which also has some excellent places on the way down, including a really accessible mangrove swamp.
The best info is available here: http://www.thaibirding.com
It is about 1hr south of Bangkok or 30 minutes North of Pattaya. There is a good range of habitat (water, grassland, light woodland). An early morning visit would be quite productive and you can easily pick up many of the birds on the list (and I've seen a few not on the list too).
Re Pattaya. Yes it's a bit sleazy (OK - a lot sleazy in some areas) but it's interesting and I wouldn't discourage you from visiting. There are easy day trips to some nice islands and a really nice beach called Navy Beach just a 20 minute drive South down the coast. Hotels are many from cheap and grotty to very upmarket and there is plenty to see see and do away from the gogo bars and other adult entertainment.
Different people have different ideas of what they mean by the "Bangkok area". As a resident of Bangkok since 2004 I consider that to means pretty much the city limits, but if I'm coming from the far side of the world I might be thinking on a slightly grander scale, and places like Khao Yai National Park (2-3 hours drive) and Kaeng Krachan National Park (3-4 hours drive) might fit into that definition.
Both of these national park offer great birding in June (wet season) so I would recommend those sites to a Canadian making a first visit to Thailand.
For beaches, it depends on how long you have got - personally I'd recommend jumping on an overnight train to Chumphon and getting yourself on a ferry from there to Kho Tao, or stay on the train to Surat Thai and then get a bus to Krabi. If time is more limited then the beaches at Hua Hin may be a better bet, but they are nothing when compared to the beaches further south. You could always fly on one of the budget airlines to Krabi to save time. Krabi Mangroves in June is a very good bet for Mangrove Pitta.