Basic rule of thumb is that if you want a mount that works, get yourself a Bobro Engineering or LaRue mounts, and stay away from ARMS mounts.
Sadly, for EOTech magnifier LaRue only makes a short mount, LT670-EO (
http://s tores.homestead.com/Laruetactical/Detail.bok?no=270 ), that presumes that you mount your EOTech 512 onto the rail, without using LT-110 EOTech mount.
I use an EOTech M550 in conjunction with Aimpoint 3x magnifier, and I have only positive things to say about LaRue LT-110 mount for EOTech in conjunction with LT-649T cantilever mount (
http://s tores.homestead.com/Laruetactical/Detail.bok?no=171) for the Aimpoint.
Now, obtaining LaRue in Canada is problematic, since Mark LaRue won't export (so you have to export yourself, or get someone to export it for you). Does that mean that you should compromise? It's a decision you will have to make for yourself.
You didn't mention if your EOTech magnifier is 3x or 4x with built in ARMS cantilever mount. I would, strongly caution against ARMS mounts. In my experience, they are a Stück Scheiße (pardon my bad German) made out of pot metal.
In fact, I'd refer you to the two threads on arf:
http://ww w.ar15.com/forums/topic.html?b=2&f=219&t=179975
http://ww w.ar15.com/forums/topic.html?b=2&f=219&t=182242
If you haven't yet bought an EOTech magnifier, and just exploring the options, seriously, I urge you to look at the Aimpoint 3x and LT-649T mount combination. Chances are you will be very happy (Your wallet on the other hand might be not as happy).
P.S. FabSports has LT-110s:
http://www.fabsports.ca/MOUNT/ar15/LT-110.html for 175$ each. So 200$ on EE might or might not be a deal (depending on taxes).