I've done both the OSA (actually MilCun) and the ORA courses, both are excellent with very good instructors.
The MilCun facilities are awesome, and there is more shooting on the MilCun course, including shooting at gongs and other reactive targets at 600M which I have not been able to try anywhere else. The MilCun course is 5 contiguous days of sustained learning and practicing so you are "focusing on performance" for the whole week.
On the ORA course the last session is at CFB Borden so you get to shoot on a military range. The classroom and indoor practice are at Burlington which is a 50 yard range but they make good use of it for fitting rifles, getting familiar with scope adjustments (including wind which is created by the instructors) and other prep work.
You can't go wrong with either one of these, if you are interested in long range shooting and can afford the time and fees I highly recommend both.
As is usually the case with courses the more you can do to prepare yourself and your equipment, ammunition, etc. the better. I believe the requirement at MilCun is a rifle, bipod, scope and ammunition that will shoot a 1" group at 100 yards.
At the MilCun course there is some support available for equipment issues but it is always better to come prepared for anything, I took lots of ammunition and a spare rifle + scope.
For both courses a spare brain will be needed for when yours overfills.
Snapshot