Like YYZprincess said, if you don't have status (or have purchased E+ access for $299) on United, E+ is not in general available. Even at check-in. While they might be willing to upsell at check in, you can't count on it.

Also, be aware that even if you buy a W fare, a) upgrading with a SWU is not guaranteed - it might not clear, and with no status on UA, you're near the bottom of the list, and b) you have to get a SWU. These are normally issues to 1K's and higher.

If you have enough Air Canada miles, you will be able to upgrade Economy to Business (again, subject to availability, and you will not be near the top of this list) if you upfare to a B. This will probably cost well over $1000.