The Canadian show follows pretty much the same formula. You don't need to have seen anything; there's no continuity outside of the individual seasons.

I think the quality of baking is higher in GBBO, especially in later seasons, but that doesn't really change how the show works. It just makes judging (and guessing who's going to lose) harder.

I can't answer the first one properly since I haven't seen the British one, but it seems similar from the clips I've seen?

Do I need to rewatch from season 1 to get things/jokes?

Nope, they explain any weird rules/procedures when they need to

Anything to keep in mind while I watch?

Nothing comes to mind, it's a low stress and wholesome show that I like to watch with family :)