Ski-Doo Snowmobile Challenge

For this achievement you need unlock everything in the career, this includes: Race events, sleds and rider outfits.

Winning every event is not necessary to unlock everything but is recommended so that you rank up more to unlock the last outfit for your rider at rank 20.

To unlock all of the race events you need to come at least 3^rd though you will need to come first in certain events to unlock the sleds.
The events that you must come 1^st in are:
Duluth SX
Duluth National
Air Masters (You need to win this event in 2:30 or under, so the clock must be above 0:50 when you finish)
Pit Challenge
Swedish Cup
Quebec Open
Yellow Run
Stunt Challenge (You need to win this event in 2:30 or under, so the clock must be above 0:50 when you finish)
Nordic Climb
Yukon National
Whitehorse XC
Snow Bowl X
Hill Challenge
Demon Cup
Ice Men's XC
Valcourt GP
West Side Cup

Always aim for at least 3^rd in every race so you can progress through the career but 1^st is what you ideally want.
You can retry events with better sleds later in the game.

You can check what is left to unlock via the Race menu, Garage (Select sled) and Dress Rider menus.