Well there are a few things you should be aware of.
a) Chinese manufacturers cannot believe how big Westerners are. Don't order unless there are measurements given (not just sizes) and even then go up a size or two.
b) If something is wrong with your purchase, eBay will require that it be returned for a refund with tracking. Tracked shipping to China starts around $40, so if you don't like it, plan to donate it and save money. Or give it to your ten year old niece.
c) Free Shipping is quite common from Asian sellers. But Free Shipping is adspeak for 'the cost of shipping is included in the price of the garment'. So reduce the price by some guesstimate of shipping cost to get an idea of the quality of what you are buying.
Most Chinese sellers are honest and try to do a good job. However:
d) Anything under 99% positive FB is bloody awful feedback. And read the negative comments. This will give you an idea of the problems. 'Slow shipping' means they use Surface shipping and you won't see your item for months, well past the deadline for eBay Disputes and refunds. 'Poor quality' should be self-explanatory.
e) Some sellers don't ship anything and then promise a replacement when you complain. They don't send a replacement either.
f) NEVER BUY A WEDDING DRESS FROM CHINA. It won't arrive on time, or will be much lower quality than you expect, or will not fit.
But in answer to your actual question, Canadian duty and sales taxes start at $20CDN (approx $16USD) value,not including shipping cost. But CBSA and Canada Post tend to ignore parcels valued under $100 that are not bulky on the sensible basis that it would cost more to collect duty and tax than would be collected.
But don't count on it.
