Why stop it? If they want to recruit, fine. But don‘t be hypocrites about it. Open up the borders. If a Yank wants to serve with us, fine. If we want to go there, fine. Citizenship should be separate. And as for the security argument. Get serious. It‘s up the the relevant agencies to perform the security checks as part of the application process. If anything, they should enjoy having the odd undesirable coming to them and being revealed.
If the CF wants to prevent this loss of potential talent to the US, then the Government has to provide the resources to make the committment to the CF competetive with that of our allies. If they do not, then do not be surprised when people choose to opt for a military that appears to provide many of the incentives that they desire over that of their parent nation.
Isn‘t that supposed to be the point, we are all "free" to choose our paths for ourselves?