No, that's not the assumption made by the economic model.
The assumption was twofold. First of all, they assumed that wages within Canada were perfectly equal across every sector of the economy. The importance of this is that it underestimates the importance of losing a well-paid job in the auto industry. We all know that a displaced auto worker may indeed find work again some day--at Wal-Mart or at Tim Hortons--but it's the decline in their income that really matters. The economic model from the government has assumed that this cannot happen because everyone is paid the same.
Second, the model makes the assumption that the whole country is one big household that shares equally in all of the income that all the different industries generate. The distributional effects of a free trade agreement are also ignored.
Those are the two very strange assumptions made by the model.