What kind of Canadian VIsa are you holding? If it is just a TRV, it will be hard to apply as even your status in Canada is not stable.
However, if you are holding a work or study permit validation which is longer than one year period, I believe you will get a US Visa easily. I tried couple times before without any trouble.
BTW, you don't need to apply for re-entry visa to get back from the States ONLY.