A high gain cellular antenna on a pole or tower may be the way to go. It would require a device with an external antenna connection and a suitable antenna such as a dish or yagi designed for the band being used. It would need to be aimed at the nearest cell tower, preferably with line of sight.
A cellular repeater would extend cell phone coverage to all nearby devices such as cellular modems and phones. There is an existing thread on this here. Be sure to verify that any device purchased is suitable for the local service type.
Looking at the maps, I noticed there's two Ril Lakes. One of them is NW of Hearst, at this Google Maps location. That Ril Lake is outside both Rogers and Bell's coverage maps, and is the location I was looking at yesterday.
The second Ril Lake is located here, near Lake of Bays. This area is within the coverage maps of Bell and Rogers, and if you can get a signal should be able to get HSPA+ internet speeds. The 15 foot USB cable is probably your best chance for achieving a signal at this location.