$870,000 is the AAV. They don't say this officially in the release above, but this deal begins this year. Two years is the duration because of Webber's age as mandated by the CBA.
Webber is reportedly with the Leafs already in Tampa, and it seems his role will be to stay with the NHL club for now. Because they traded for his rights at the deadline, he is playoff eligible for the Leafs.
To make cap space, someone will have been papered down to the AHL, but they will return when the season is officially over and the salary cap goes away.
This article contains some limited information on Webber:
Welcome to the Leafs, Cade.
At the same time, Webber's teammate Sam Stevens was signed to and AHL deal: