Firstly, are you an ATCO with a valid licence (presumably working somewhere in the UK) or an ab-initio?
If you are the former then you would apply through the Experienced Controllers Program which, unfortunately, no longer exists. That's not to say they no longer employ foreign controllers, I'm just not sure how one gets in these days.
If you are the latter then you must be a Canadian citizen or a Permanent Residency holder; all that you have read on the recruiting website would then apply to you.