Bases upon what we have seen up to this point, I would not be surprised to see Shaw start out the season at Iowa.
As far as his getting to the majors next year as the Cubs third baseman, I would think that if the Cubs were seriously thinking about that, they would have had him play a lot more at third base already this year. Of course, things could change.
The cubs have enough uncertainties next year (third base, first base, DH) that there is no reason not to try to sign Candelario, if the money is reasonable, assuming that there are no better players options available.
But I think that the main thrust of the off season should be trying to upgrade the pitching staff, even if for some reason, Stroman should remain.