It's already being done - all the commonwealth citizens in the armed forces. RAF has significant number of KIWI piolts and air crew that transfered after New Zealand cut its airforce dramatically.
Wonder how many Canadians would be interested? All the ones I've worked with,love it here. Not sure if it's still true about CDF or whatever they've called this week, but some of them were interested in a Brit Army career.....
I served with Kenyan's, South Africans, Kiwi's, Australians and bloody Canadians all decided that thier best chance of seeing some real action was to join the good old British Army, on the same note I had a mate who transfered the other way and left the Engineers to join the Aussie Engineer corps. :-/ Better weather or something