Are you on such expensive medications that you can not pay for them for 3 months? Do you have insurance where you live currently and can you get your doctor there to prescribe you a 3 month dosage you can take with you to Canada? 6 months dosage would be better. In order to get on your medications in Canada, you need to find a doctor in Canada to prescribe them, depending on where you are from, you may not get exactly the same ones here, different brands maybe but it should all get worked out.
Most employers offer supplemental health insurance as a part of the benefits package, covering medications or some part of the cost but you may have to pay for a part of that insurance. Small employers may not do this but then you can buy your own supplemental insurance. Where I work, the employer pays for a part of the insurance, the employee pays $40 a month, the insurance kicks in 4 months after starting to work there and pays 90% of medication costs and many other things. I know somebody who pays for his own insurance because his employer doesn't do it and he said he pays around the same, $40 a month but I think his only covers 70 or 80% of medications and way less other things. There is still a qualifying time when you get on an insurance plan like that when they don't pay so I am not sure if you can get on one right away.