I need to get this out of the way.
Canada
Leader: Pierre Trudeau
UA: From Sea to Sea
10%+ from trade route income, Canada and civilization with a trade deal gets +5% growth rate on all cities.
UU: Mountie
Calvary Replacement, starts with Sentry (+1 Sight), City with Mountie garrison gets +1 happiness, +10% against enemy spy efficiency.
UI: Sugarbush
Available at Trapping, can only be built on forest, +1

+1

, Receives all the bonus given to trading post (+1 gold with economics, +1 gold with Commerce tree finish)
so basically, a trading post with food bonus that can only be built on forests.
I want a wide civilization that plays peacefully, with incentive for maxing out Commerce, and right side of Honor.
This is why I want another run of DLC, because Canada being the expansion pack would turn people away from the expansion pack, but as DLC it would be more acceptable, plus it would sell well with so many Canadian Civ players.
Kudos on the sugarbush UI, which I also had in mind. Mountie was my choice as well (with the name "RCMP"), even though it's a controversial pick, and like you I feel it would be cool to have a unit that gives a bonus with garrison.
For the sake of thoroughness, and having somewhere to put these down, here are my ideas:
UA: Strong and Free - a UA that partially closes the gap in raw strength between units when the Canadian one has less (say the Canadian unit gets 50% of the gap with a max of +20 strength), and allows 50% faster (by culture) and cheaper (by gold) acquisition of tundra and snow tiles. Start bias: near tundra.
The reasoning on the first part is that Canada can spend less on military development and still be able to properly defend and conduct peace missions. It also prefers a small number of highly promoted units, since the gap it closes is the
raw strength gap before bonuses and penalties. Then again there are probably a lot of interesting ways to incorporate the new features once more info is known.
Those trade bonuses would be fine for me, and From Sea To Sea is a great UA name.
UU: RCMP (Cavalry) - Lower strength than cavalry, but gets a strength bonus that makes up for it when in friendly territory. +1 culture (or "tourism") and 25% slower spies in garrisoned cities. Doesn't obsolete, and promotions are lost when upgraded.
UI: Sugarbush - ...pretty much the same. Being able to trade maple syrup would be cool, if the trading system were somehow changed to accommodate this without being cumbersome or OP.
Finally, for the leader and name. For the leader, I feel it's a toss-up between Trudeau and MacDonald. For the name, there was a mod that called it "Dominion of Canada", which sounds like a Civ-worthy name in my book.