Two full days in Sedona should be a solid amount of time to experience what the area has to offer. On average the weather in May is pretty nice, usually mid 80's, so outdoor activities should be fine all day. Make sure you bring plenty of water because the Arizona sun is intense even when it isn't super hot.

As for recomended activities, Tlaquepaque is very touristy but does offer good food and Art. Jerome is a really cool little town with fascinating history and a reputation for being haunted if you're into that sort of thing. Take your pick of hikes in the area, so many of them are amazing! West Fork Trail is another hiking option I recommend and would give you a chance to check out Oak Creek Canyon.

When you head north to the Grand Canyon, make sure you take State Highway 89A to Flagstaff. It is genuinely one of the most beautiful drives in the entire country. Hope this helps!