What are you trying to do with the printer?
Are you trying to produce high-quality, but run-of-the-prints, using standard inksets and media, similar to the prints you can get at any high-quality commercial print lab?
Or are you trying to do something a bit out of the ordinary, e.g. with nonstandard inks (dye sub, Piezography, expanded gamut, fluorescent inks) or nonstandard media (printing on metal sheets, uncoated paper, non-inkjet fabric, etc.).
If the former, I'd go for the Canon. You'll get better reliability, cheaper maintenance, no clogs, equal print quality and better longevity (using the standard inkset). However, due to the curved paper path, you won't be able to print on rigid media. Also, unless you're printing commercially and need the ease of use, the ipf6300 is cheaper (second-hand) and gives equal results. You could even get an ipf8300 (44" model) second-hand for the price of a new ipf6400.
If you don't want to produce standard prints, there's really no alternative to the Epson. Unlike with the Canon, it can run most non-standard inksets (including mixing and matching from different sets), has a straight paper path and is generally much more customisable. On the downside, it's a pig of a printer to deal with, with many issues that are well-documented, both on this forum and elsewhere.