I'd say it might be more difficult since your goslings are older and larger than your ducklings.
I've successfully raised ducks, muscovies, and goslings together, more than once. As long as the size difference isn't too great, everyone tends to get along just fine and they bond like one flock. It can make things "interesting" during breeding seasons later though, but it usually sorts itself out without too much drama. Usually.
If there's a big size difference between anybody though, it doesn't usually work well. And your goslings are just going to keep growing too. If you want to keep trying, I'd say make sure they have enough space, and maybe even a way for the Pekins to get away (maybe something smaller they can squeeze through or behind - though you'll have to constantly resize that). Things might settle down for you.
The age difference isn't TOO great. I'm not really familiar with the size or growth rate of Canadians, specifically, and whether your Pekins are the really large ones or not may make a difference.
I hope it works out, or you find a solution.