Oh man, a wedding in Seattle this Saturday?? That is gonna be so beautiful but yeah, you definitely need a flash that wont quit on you in the middle of the ceremony! I have been using the 5D Mark IV for years and it is such a tank, so you really want something that matches that level of reliability. Honestly, if this was just a hobby shoot i would say go cheap, but for a wedding? You gotta go with the Canon Speedlite 600EX II-RT Radio Wireless Flash! I love it so much because the weather sealing is incredible and it just... works. Every single time. Here is the breakdown from my experience:

• Canon 600EX II-RT: Super fast recycle times and the build quality is basically bulletproof. It feels like it was made for the 5D line! Total life saver when it starts drizzling.
• Godox V1-C Li-ion Round Head Flash for Canon: The round head gives amazing soft light and that battery lasts forever, which is fantastic! But... I have seen the hotshoe mount snap on these way too easily during high-pressure gigs. Its a bit of a gamble.
• Profoto A1X AirTTL-C for Canon: If you really want to splurge for total peace of mind, this is the gold standard, but it is pricey as heck! Seriously though, stick with the Canon for this weekend! Nothing beats that native compatibility when you are rushing to catch the kiss or the first dance. You dont want to be fiddling with a maybe flash when the pressure is on. Good luck in Seattle, it is gonna be amazing!!

I totally feel your stress right now! I actually had a similar crisis last year during a super hectic wedding shoot and realized having a li-ion battery is a total lifesaver. Go with the Godox! I absolutely love the Godox V860III-C Li-ion Camera Flash for Canon because the battery lasts forever and it recycled so much faster than my old AA units! It worked perfectly with my 5D IV. Since you are in Seattle, definitely watch out for the moisture tho... I once had a flash glitch out from just a bit of heavy mist. Two quick tips for your shoot:

• Grab a spare Godox VB26A Replacement Li-ion Battery just in case.
• Test your high-speed sync outdoors if it is a bright but overcast day! Honestly the Godox system is just amazing for the price and you wont regret the switch from the expensive Canon brand gear. Good luck this weekend, you are gonna crush it!

Lol I was literally about to post the same thing. Glad someone else brought it up.