Hi and welcome.
There are quite a few Canadians here. As far as I know, there is a Gamma Knife Centre in Winnipeg, but this is probably not an option for you if your AN is large. Did they say how large it is? Other than that, I don't think there is much expertise in the prairies. I haven't heard of anyone who had treatment there. Expertise is key, and you need to get access to an experienced team. This means that you probably have to travel. The most well known centres in the East are in Toronto (University Health Network including Toronto General and Toronto Western (Drs. Rutka/Tymianski, Cusimano, as well as Sunnybrook (Drs. Chen/Pirouzmand), Ottawa, Montreal. There is also Dr. Akagami at Vancouver General, there are quite a few of us (me included) who had surgery with him and had excellent outcomes.
Make sure to research your options and ask for referrals, so that you can choose the team that you feel more comfortable with. Travel can be very inconvenient, but unfortunately may be necessary to find an experienced team.