Can anyone please explain the mechanics behind Muscovy and Tver getting Colonialism without bordering any province that already have it?
You can click on a province they own and in the institutionstab see the reasons for the spread. As there are now already bordering provinces which have it, that´s the most likely reason it continues.
As for the getting the institution: I´d guess that either muscovy got a CN (rather unlikely, as they appear landlocked), one of them has an ally who embraced it and decided to share the knowledge, or, and I think that is most likely, the small Tver which couldnt expand reasonably decided to spend it´s monarch points to develop provinces and got the institution that way.
So I just had a bit of an off-the-wall idea.
Forming France as England. I find the PU war quite doable, there's a double chance of the Burgundian inheritance and then we can beat up Castile/Portugal to get quicker access to the Caribbean and PU them after.
Am I missing any obstacle to this? I know I cannot form GB if I want to form France.
Well, since forming France needs the country to have either French, Basque or Breton culture, I guess you´d have to culture shift, since Breton isnt the same as english

Otherwise you can just form it once you own the neccessary provinces:
Form France in Wiki