Stay east of the city center (Longueuil or Brossard): this made getting out of the track SO much faster and easier
This relates to #1 but you will need a car or be willing to pay for Ubers if you aren't in downtown. We took the metro from Longueuil and there was parking there. Ubers on race day were around $80, parking at the metro was $25 per day (you cannot drive or park at the track)
There are two bridges in and out of the track island. Everyone goes to one of them, making it super crowded, so try to find the other one
Water filling stations are few but are available, there are lines to them. Water is like $10 so bring water bottles
Get a metro pass BEFORE Friday cause it gets crowded at the station during the weekend, the metro is the only way to the track
Downtown Montreal is pretty and worth spending time in. Great food, lots of merch (but hella expensive), lots of cute stores
Buy ponchos at the dollar store and order seat covers from amazon. They were so great to have. We had ones with backs and they didn't bother those behind us and were comfy for us
Buy tickets from the actual GP website. This gives you access early for the following year. Keep checking ALL the time. they release ones without saying so. We got ours in April. gootickets is another great source
pit lane walk is NOT WORTH IT. the way it's set up and how oversold it is makes the experience is horrible. it's too crowded, people stay put in front of the garages without moving, unless you get there at 6am, it's not worth it you wont see shit
Brush up on very basic french. all signs everyone outside of the track are in french. but people DO speak English if you have to ask
bring hoodies, it gets cold
don't bother going if you want to get GA. it's muddy and you will not be able to see shit. and if you can, select a grandstand by a screen
be prepared for long walks. from the station to our grandstand (turns 6 and 7) was about 30 mins! it’s longer to the main grandstand