How can canadians get the taxes back they paid while in the US?

You probably mean the Sales Tax you paid. It is not like the GST or VAT in Canada....this is an entirely different system. It is a tax on the entire sales price, administered at a local level. Not a National tax on basically on the value added by that part of the distribution system. It is applicable to any purchase, by anyone (unless perhaps you were charged it on a large item that you were buying with the first use going to be outside the US, for export - and even then just picking it up in the US is frequently considered first use). In that case you should speak with the one who collected it and they should provide the documents you need to prove it is for export and give a refund. Otherwise, it would not be refundable.