Lots of room for speculation on that question. I think some of it is already priced in (my guess is about $1.50). Some of the current investors bought this stock expecting the home building and distribution parts to be sold at some point. Many investors will wait for a sales announcement before jumping in; others will wait to hear WY's plans on what to do with the money. If they use the proceeds to pay off debt we'll see a small rise. If there is a special dividend then we'll see a better jump.
I would suspect WY will use the proceeds to substantially help finance the 2.65B acquisition of Longview Timber. Weyerhaeuser financed that deal by raising about $2.45 billion through selling debt and equity and a bridge loan facility with Morgan Stanley. I'm sure WY wants to pay off that bridge loan as the rates are notoriously high.