Your brother's a 3rd year med student currently, so this means you are planning a July 2018 wedding? Or is he a fourth year and going thru the match and interviewing this year? Just clarifying the timeframe here.
Honestly, it seems like a stretch to anticipate he can get the weekend of July 1 off. Obviously there are some programs that are more accommodating than others, but I would not assume it will go your way. July 8 might be easier depending on the program. However, if he is currently a 3rd year and just starting clinical rotations, he may end up liking a different field altogether. Some fields are more or less likely to be flexible--the bigger the program, often the easier it is to accommodate.
There are several things to consider here as well:
1. He may match somewhere far away from where you're getting married. Odds are high that the week before your wedding, he will be in orientation/working/etc.; even if he is off that entire weekend (which may be a long shot), he still will need time off to travel.
2. Is he standing up in your wedding? The more days off he needs off during this timeframe, the harder it is to accommodate.
3. Have you talked to your brother about this? I know I personally would have felt very uncomfortable calling my PD after the match and trying to get off work the first weekend (and I would have been told NO) and worried about whether this would start me off on the wrong foot. At that point, I didn't know my PD and had no idea how vacation weeks and other requests were determined. And if he absolutely can't be off, how will you and other family members react? Given the timing of the match, it will be too late for you to easily change wedding plans as well.
4. Keep in mind that if he is told no, quitting and finding a different residency slot (and one that would allow him off when he wants) is not going to be an option for him. And would be a match violation for him to quit (if NRMP), which would severely limit residency and fellowship options for years to come. I find that people outside of medicine do not understand that residency does not work like a normal job.