Just for all the nay-sayers:
I personally own and drive a 1998 Subaru Outback and use it to tow my 2006 Ski-Doo MXZ 800, and sometimes a second sled too. I shred in the Whistler area and have used my car to town my sled up and down logging roads and in the snow.
That being said, purely for hauling the sled (and especially 2 sleds!) it is a less than ideal set up. It definitely got the job done for me all winter, but it also put hella strain on my clutch/transmission. The STI will tow your sled(s) but it will be a drain on its life. I personally don't give a fuck and am happy driving my car into the ground (though I would love to extend its useful life as much as possible). There are many times when I have bottomed out and my suspension is kinda fucked too (but that's mostly from rally racing logging roads in the summer). When it comes to late spring shredding, forget about it. You need a bad ass truck to get that high on many of the access trails. During deep winter, when the snow level is low, the subaru is fine, but you will probably have to cut your sled season shorter than if you have a truck. I'm fine with it cause I just transition into mountain bike, kayak, tennis, and cliff jumping season.
I would be pretty damn stoked to upgrade to a nice turbo diesel truck. A late 2000s Dodge Ram 3500 cummins would be REAL nice, even a 2500. The truck does have its down sides too. It's expensive as fuck to run, it's a bitch to park, and you're not going to look very cool unless you have some 30 inch tires. Plus your sled has to be bad ass enough to match the truck. You'll need at least a 2008 XP or preferably a 2011 E-Tec. But if you are ready to step it up like that, you will be a champion among men.
Get the truck. The Subaru WILL and DOES get the job done, but the truck is superior and you can just ride a dirt bike in the summer for your kicks anyways.