Ski-Doo Snowmobile Challenge is not particularly long, but can be quite challenging and even frustrating at times. Some of the later races in particular require a nearly perfect race in order to win, which will result in a lot of repeated tries. But the main reason for the 3-star difficulty is the online trophies which, given the age of the game, is quite hard to find anyone and fulfill their requirements legitimately. However, if you have a boosting partner, the difficulty rating could be brought down to a 2-star.

The Platinum technically only requires about 15 hours of gameplay, though it depends heavily on your skills, as well as your ability to find anyone online to play with.

You can begin things by playing on Career mode. Coming in first place will unlock things such as new tracks and snowmobiles, so be sure to keep racing until you come in first, before moving onto the next race. Unlocking all the unlockables will earn you both the Hoarder and Pack Rat trophies. Also, try not to spend any money until you've collected $50,000 and unlocked the Stingy trophy. During your playthrough, at some point work on unlocking the Untouchable trophy for winning a race without crashing. Also, if you want, you can spend time nabbing the Woodcutter trophy for colliding into three trees in one race, and Crowdsurfing for colliding into the spectators.

Next, is basically just mopping-up the remaining trophies offline. There are a few which are easier to perform in two-player co-op if you have a second controller, such as Roadrunner for leading the race from start to finish, both the Adrenaline Junkie and Boostaholic trophies for remaining in adrenaline mode for a total of 60 seconds, and the Bully, Berzerk, and Rampage trophies for taking down a total of four opponents in a row without crashing. Be sure to check out the Ski-Doo Snowmobile Challenge trophy guide links under our Links tab to see what you need and their requirements.

There are two online trophies which can be unlocked at anytime: Friendly for sending an invite, and Online Acrobat for achieving 20,000 stunt points in one online race. Given both the age and unpopularity of this game, you might have some trouble finding players. If so, be sure to check out the boosting forums under our Links tab.

chucknorris078 has a great Trophy Guide here:
http://www.playstationtrophies.org/game/ski-doo-snowmobile-challenge/guide/

A great Trophy Guide by lordmartock:
http://ps3imports.org/forum/index.php?/topic/145-ski-doo-snowmobile-challenge-trophy-guide-road-map/

And a useful Trophy Guide created by trophybot:
http://ps3trophies.com/forums/showwiki.php?title=PS3-Trophy-Guides:Ski-Doo-Snowmobile-Challenge-Trophy-Guide

And an Achievement Guide (nearly same as trophies on PS3) by Pashos:
http://www.xboxachievements.com/game/ski-doo-snowmobile-challenge/guide/

Here's a Boosting Forum on PlaystationTrophies:
http://www.playstationtrophies.org/forum/ski-doo-snowmobile-challenge/9744-trophy-boosting-thread-read-first-post.html

And a Boosting Forum on PS3Trophies:
http://ps3trophies.com/forums/ski-doo-snowmobile-challenge/1307-official-ski-doo-snowmobile-challenge-boosting-thread.html

Lastly, here's a basic Trophy List:
https://psnprofiles.com/trophies/347-ski-doo-snowmobile-challenge