Where to get First Aid/CPR training?

Red Cross.

you can also check lifesaving society website to see courses available.
http://www.lifesavingsociety.com/find-a-course.aspx

Red Cross is another affiliate.
You can also check St. John Ambulance as well.

check the city of toronto website

some security places have it included as part of their course.
one of family members did their security course here(link below) and the aid/cpr thing was included.

example: http://www.centreforsecurity.com/

I'm assuming you've completed all other parts of the security training programme, namely the Use-of-Force training. Btw, I don't think these guys do it cheaper (it's around $90) but they're licensed and certified by the Ministry of Community Safety. And, all licensed agencies will award you Canadian Red Cross and First Aid certificate upon completion. Good luck on your career!