You heard that right, whether you own the game or not, sign in with your Uplay account and you can play the multiplayer component of Trials Fusion completely free this weekend.
The multiplayer mode is a forthcoming free update where up to 8 players can race across a level to be the first across the line. While the update is coming to all currently supported formats the free multiplayer weekend is PC only.
It should be available right now. Go go go!