I may be late to the party in this thread, however: The best tires from my experience have been Toyo M-55. These are a 'commercial traction' grade tire, and they are LEGENDARY in the oil patch, construction, pipeline and wireline industries for durability, longevity, and good traction characteristics on and off-road.
The kicker is that they don't come in 20" sizes, but do exist in the factory 17" size of 265/70-17.
I run a construction company in Fort McMurray, and wouldn't have anything else on work trucks. There are better tires for pure Alberta Gumbo (the 'special' kind of mud we all love to hate... I believe it's 'alluvial clay' for you geologists), but they sacrifice a lot in other areas. They are every bit the match of any other non-dedicated mud type tire. The M-55 is also as heavy as the winter is long, and ride like iron-clad wooden wagon wheels, and howl on the highway like a tortured Galloway cross, but they're nearly indestructible. Driving on sites full of screws, nails and rebar, I have yet to poke a hole in one. I can't say this for any other tire I've tried, including BFG, Firestone, and numerous models of Goodyear.
These tires are widely available at Kal Tire stores.
Some other free advice (which may or may not be worth the asking price): rather than a whole month's worth of food (unless he's carrying supplies for his whole time in the field?), he should thoughtfully assemble a 72 hour 'get home bag' with sufficient rations and gear to weather a couple of days in total isolation. If said bag can include a satellite phone, he probably won't ever find himself stranded beyond his means.
If predators are a real concern, my best advice is to invest some time and funds in a firearms license, a non-restricted class firearm (a 12 gauge shotgun would be my first and last recommendation) and ample practice. (I am a lead instructor for the Canadian Firearms Safety Course - the required course to receive a license in Canada, and can offer more info via PM if required).
If his conditions of employment preclude the possession of a firearm, pepper spray sold at outdoor stores for bear deterrent can be effective against Ursine and Canine species, but it has proved marginal for Feline predators such as Puma Concolor - the common cougar or mountain lion.
Good luck!