We have had a string of Canadian Generals get developmental assignments with US Forces over the years. Deputy CG of Third Corps at Ft.Hood, or DCG of a US Division is not uncommon. It gives Canadian officers an additional opportunity for promotion and higher level experience, while keeping a warm bench of talent, in case of contingency.
A lot of planning and prep goes into making sure that US and Canadian forces are interoperable, so we can work together when needed - including developing people. If a particularly good Canadian is noted coming up in the ranks, they can sometimes make even an extra space in a senior command. NORAD is a relationship like we have with no other country.