There were rumours of a "gentleman's agreement" between Nav and NATS which stopped the flow from the UK in 2005-ish.
I was the last controller to go through the experienced controller program...it had unofficially stopped when I applied...had to go through a side door to get accepted. The rumours were pretty much true. Since then any controllers from abroad have had to apply through the regular stream...as odd as that is!
NAV CANADA no longer has an Experienced Controller Program as the results have not met our expectations
As Cossack said..this statement is a bit of smoke and mirrors. All the foreign controllers that came to YYZ checked out within a year (myself included).
There were problems at other ACCs which have been discussed on other threads. These other ACCs had/have low checkout rates aswell...and supposedly the foreign controllers could not adapt...or had lied about their qualifications (according to one poster previously). As I said at the time...to qualify for the program you had to have an ATC licence...which from the UK meant you had gone through some pretty thorough training and your validations were there to see.
Read into the "results" Canada wide as you will.
The worst thing about applying from scratch now (if you are already a controller) is you won't get paid till you reach an operational position. I can't think of many experienced controllers that would forgo a years pay just to move to Canada.