[SonicScrub]

I can't speak for the other nations, but Space technology in Canada is controlled under the Controlled Goods Program (CGP). A CGP clearance is obtainable as a Permanent Resident. No citizenship required. Various Canadian companies are suppliers/partners for space projects in the US. For example the Artemis project is using the Canadian company MDA as a key supplier (to manufacture space robotic systems, including a newer version of the robotic arm currently on the ISS). SpaceX also has a number of Canadian suppliers, although their involvement is not advertised very much.

[colordrops]

The US is the same. You don't need to be a citizen to work an ITAR controlled job. A green card will suffice.