If you have offer letter of Manitoba school, then apply for study permit extension based on that that Offer letter. Take profile statement from your bank and apply for study permit extension. You need not to have 4 months bank statement. If you have paid fees for your january Course in Manitoba, then attach with it. There is no problem in study permit extension. And I assume your course ends up in September then apply for study permit extension before 90 dyas. And your course if starting after 4 months then you can work on SIN in this period for first 150 days after applying study permit extension.