It will certainly not be substantially better than the Vega56, if that is what you're asking. I would either wait for reviews, or just go with a 2070 (that's roughly Vega64- or 1080-level performance).
But, in any case, I would stay away from Gigabyte. I would go with either a MSI or EVGA card.
The price on the RX580 is high - about $100 more than on newegg.ca, so it will be hard to compare value based on this listing. Performance is rumored to be about 1070~1070Ti range, so if it is price comparable to a 580x in Canada, that'd be a good deal. However, the Asus card listed is one of the most expensive RX580's available, there are many available for >$100 less. Again, check newegg.ca