When doing outdoor portraits, I like to get the sun behind the subject and to a side, then pop a strobe off camera, bare or in an umbrella crossing light (180 degrees opposite or nearly opposite) with the sun. In this configuration, the sun provides the rim light, and your strobe can be a controlled main light.

The color of the strobe will often match bright sun enough, but if it appears too blue, add an 1/8 or 1/4 CTO gel to warm up the flash.

Assuming the groom is in black and the bride is in white, you may want to start with the groom nearer the strobe to avoid overexposing the bride's dress.

Alternatively, shoot in the shade, and use the strobe for a bit of a highlight.

Scout the venue first, preferably with the Bride & Groom.

Decide exactly where you're going to be standing, what direction you'll be facing & at what time of day... you should be able to get a good indication of where the sun will be for the actual shoot.

If it's behind them, then yeah, I'd suggest some fill flash or if you have a second flash & reflector/umbrella that you can trigger off to the side, it'll probably soften things up a bit.

Probably worth shooting bracketed shots as well & shoot in RAW in case the amount of sunlight changes with cloud cover moving in and out.

I agree with Eoin and I'll emphasize the reflectors. You'll want big ones that can be hand-held and reflect natural sunlight over flash. Most likely the gold coloured ones that will give you a less harsh light would be better. Bear in mind that the bride will definitely appreciate the warm and soft skin tones from something like that over the harsher tones that a flash will give.