For me too, please note black legs, just visible right head pattern, swan-like proportions with long neck (compared to Anser-Geese). I know, you maybe hesitate, because Canada are rare in Poland? They are for sure rare in NW-Poland
no narrow vertical cheek patches as in canada but diffuse pale head sides as in greylag. strong counterlight, so necks look black, but note how the light is "eating" into their sillhouette, making them thinner than they are. and proportions: in canada neck is longer than head + bill, seen from below while in these birds necks are shorter.
Thank you Lou and The Fern for comments. After looking at those pictures again, and knowing the new input, I am unsure now (thanks for that). Yes, light situation can produce a pitfall picture here, but I looked at all birds in these pictures. Is it possible, that this can result in a good, but not perfect colouration and pattern as said, including the following "pro Canada features" in all birds?
slightly paler breast with slight contrast to darker neck
gradually paler vent in slightest contrast to darker belly (which look brownish, yes colours are nearly impossible to judge)
yes colours are nearly impossible to judge, but legs look very dark and I would suspect to see paler bills, if they were Greylags, too.
I get the impression that contrast between darker underwing and paler belly (outlining division between body and wing) in some (not all) of them is better for Canada.
after reading Lous comment I looked at the underwing more closely. Greylag is said to have two-coloured underwing, but there is some variation in this and a feature very much dependent on light conditions. I am undecided here, but with a little bit of wishful thinking it might be slightly better for a Greylag indeed, but clearly within variation for Canada.
Conclusion? Is it possible to see the original pictures, and would you allow others with experience in editing to adjust colours, brightness and contrast? While I am still in the Canada-camp (ignoring that a flock of Canadas would be a good record for Poland?), I get the feeling, that I would be surprised, when seeing the corrected pictures.
Thank you Max for the original pictures, I still hope for experts to edit them, but after just enlarging them I see Greylags now. Thank you Lou for right identification. I must admit, that I thought the answer was there with confidence.