This reflects only what I've experienced - but yes, if you win the World Cup with Canada you'll also get an invite to the Confederation Cup. I have never lost the WC and been in the Confed tournament. Maybe you can 'qualify' (randomly) as the CONCACAF rep, but I've only been in as the WC rep). And I've never been in Copa - that's always, iirc, just the S. American squads.
ALSO, importantly, I have NOT QUALIFIED for the World Cup even returning to the tournament as the champ. You would think you'd get an automatic place, just like in real life, but that is not true (from my experience - b/c it happened)... so again - have those May save dates so you can go back.
I've done three WC's now in my manager mode as manager of Canada. Building up the program has been what I do basically, all my league squad recruiting is always limited to Canadian players.
Tip #1: keep multiple saves so you can always qualify (it's random)
Tip #2: recruit only from Canada
Tip #3: change domestic squads often - to avoid having the responsibility of training too many Canadian players and managing all those contracts (keep the #of players under contract low - you want space to sign ten or so from the youth squad each year)
Tip#4: sell Canadian players as soon as possible - spread them around - the CPU develops players better than you will when guys are young AND the CPU can train them earlier
Tip #5: don't train anyone under 21 or so (the progression glitch - as soon as you train someone you basically stall their physical stats... you don't want that)
Tip #6: NEVER let a Canadian player leave your team through an expiring contract b/c they will never, ever sign with you ever again (approaches will be blocked) (and you want guys back in their mid-20's so you can train the best of the lot specifically)
Tip #7: don't create players before you start your career in manager mode (the potential is messed up so every created player is going to be all-world)