I would say that Canada managed to stay loyal to the crown because for two major reasons. The first being the founding "myth" of Canada being the British loyalist colonists of the US migrating as a result of the US' revolution. Them fleeing north to a major seat of political power likely had a strengthening effect on being a willing subject to the crown than most colonies.

Secondly, Canada is something of an imperial power unto itself. There are countless stories of armies marching under the crown violently clashing with nations that existed on the continent prior to European colonization. Likewise, even other European descended colonist as well as the Métis were subjugated by British rule as the Anglophone powers expanded across the continent (e.g. Queen Anne's War, Red River Rebellion, and Fenian raids). Gaining the ability to exploit the natural resources that these other nations and colonies held.

The crown was a convenient way to gain both legitimacy from the British loyalists who settled in Canadian territory and a reliable trading partner to receive resources from in the British Canadian bids for expansion. Compared to the US, who used democratic rule to gain its own legitimacy; and who's natural resources were abundant enough to be a valuable trading partner.