All right, I've had some time to get over my initial reaction and look at this design more objectively. Setting aside my personal feelings of "lameness" which haven't entirely gone away, I think there are some very well designed and powerful abilities here.
This ability is fantastic for a player who prefers a builder play-style, by protecting against wars you're not prepared for. This means that you have, at minimum, 5 turns to rush some troops into position, so you should never be caught flat-footed. Note, though, that just because they are immune to Surprise Wars does not mean that they are immune to Joint Wars or to being the target of an Emergency, which can provide civs a free DOW (of course this means that Canada can "surprise" DOW someone else who is the target of an Emergency as well).
The bonus Favor is nice, but won't come into effect until later in the game. Unless, that is, you start grabbing GW early on, then you might be able to start racking up some extra favor within a couple eras from the start. With Favor being something you can both use to manipulate the World Congress and something you can trade to other civs, this gives Canada potentially some very effective ways to play the diplomatic game (for instance, you could veto an Emergency vs yourself...), even if not pursuing a diplomatic victory.
This is a VERY powerful improvement, actually. If you plop it down completely surrounded by snow/tundra, that's a base yield of +6 Culture, which corresponds to +6 Tourism after Flight. Add in extra Culture (and Tourism) if next to a Stadium, bonus Production and Food after Professional Sports, an Amenity, and buffing adjacent tile Appeal (which is likely to already be fairly high since Tundra and Snow tend to have higher Appeal)...you get the picture. We're going to be getting ~10+ yields from a single improvement, which will be especially nice since tundra cities will tend to have fewer citizens to work tiles (even with tundra farms).
The kicker is that it doesn't really come into its full potential until pretty late in the game, but that +6 Culture should help rocket down the Civic tree pretty quickly.
Being able to buy a National Park with gold is a tremendous advantage, which also synergizes nicely with the increased Appeal near Hockey Rinks. Canadian cities should be ROLLING in tourism in the late-game, especially since there's little else to do with all those snow tiles. Even small colonies completely surrounded by snow will still be very useful when pursuing a cultural victory, as you can place a Hockey Rink and then a couple of National Parks - and the ability to buy the tiles you need at a 50% discount (which will probably stack with the policy card...) means that you can get massive tourism yields from even the smallest cities.
I've already talked about this a bit further up, but there are a few more advantages here. Yes, tundra cities are still not going to be as good as a comparable city placed...almost anywhere else because the starting yields are just going to be lower. But, the ability to build farms on tundra will help close the gap AND will provide additional Housing simultaneously, so Canada should be able to have some moderately sized cities without too much effort.
The doubled resource accumulation when combind with free culture and ez National Parks makes going for those remote snow resources a no brainer. You don't even need to do anything else with those cities, they'll be more than paying for themselves even at 1 population. And since they'll be in remote areas Loyalty shouldn't be a huge issue. And since they will have warning for any wars, you should be able to protect them without too much trouble.
Bottom line, Canada will be very effective at playing the diplomatic and culture game with small-to-moderately sized cities from the fringes of the map. They should focus on building up a very strong economy to pay for Mounties, Settlers, and tiles, and can continue expanding throughout the late game to grab those remote strategic resources (which can in turn be sold for more Favor and Gold, and/or spent to build up a booming infrastructure or military).
Additionally, focusing on a strong economy should make the levy-as-military strategy very doable, since you don't even need a standing army to protect you if you have enough cash on hand to levy from your city-state allies, which should be easy to do since you'll have a 5-turn lead time on (almost) any invasion.
The more I think about it, the more fun I think they will be to play. Very strong economic and diplomatic game, which is just how I like to play.
