Sharply increasing immigration numbers "may" well increase GDP.  However, that should NOT be the target.   Way too much emphasis on GDP growth, not nearly enough on GDP growth per capita.  Low rates of GDP growth in a low population growth environment is not necessarily a horrible thing.....

As an aside, given the current (apparent, despite solid housing start numbers...) shortage of available housing in the Toronto and Vancouver regions....and given that immigrants tend to end up in Toronto and Vancouver....is dramatically increasing the number of immigrants really such a good idea?