I've hosted MANY small and large airsoft events over the last 5 years. Every time you run a game you assume the risk. From my years of experience I've learned that providing a pre-payment option is ineffective. Period. The economy, entry fee etc... has no bearing. Saying that, I will still offer pre-payment price reductions on my events and it will sit in escrow until the game, in the event I have to return it to the players.
A game of Border Wars' size (in terms of expense, not players) would be a very tenuous line to walk, right from the get go. Most games run without insurance and a useless piece of paper known as a waiver. Dangerous? Yes. Accepted? Yes. Cheaper to run? Most definitely.
If you want a Border Wars 'type' experience, a 2 - 3 hr drive from Toronto will take you to the Lewiston National Guard base at which they run a fantastic set of OPs every year. I suggest signing up with the Western New York Airsoft League and familiarize yourself with that group. They are good guys, with access to extremely affordable and authentic facilities. I personally attended OP: Northern Wind, and let me tell you... it is a very different airsoft experience, with switched on players, more vehicles than you can shake a stick at and new faces/terrain. Gun rentals are an option, ask Mike Haggerty for more information.
In our very own country, you have OP: Cold Front (mentioned above) at another truly unique and authentic facility. Admittedly, this one is a bit of a drive... but if you turn it into an extended road trip, you will have unforgettable airsoft action and rest assured, you will be taken care of by the Manitoba players!
Lastly, if you are looking at medium sized games, with honourable hard playing airsofters, look no further than Brian McIlmoyles FTF field. An amazing space in which to run virtually any type of scenario. If you haven't signed up for "the thirty", you will be missing out, and watch for another KillHaüs Entertainment OP in the fall.
The Big OP still exists, you just need to recce for it.
1st Ranger Platoon of Canada
Rangers Lead the Way. Most of the time.