Drive-in Wedding

Can you order a few things online?

This is a simpler yet way to decorate with less flowers and more material. Hope this solution is one that helps from the choices.

Call a Barrie-based florist and see if they could do a basic arrangement that can be easily adhered to a car's hood?

Unfortunately they are getting married in Barrie and I don't live in Toronto. Maybe i will just try and make a sign that says "congrats" or a cute pun with their last name

Stephanie's photo is very typical for a Chinese or South Asian wedding. Where is your friend getting married? If they're in the Toronto area, there are a ton of shops in Scarborough and North York that cater to cultural weddings and would have pre-made things of this sort that you can just slap on the car.

This looks simple (without the flowers):

Or, here's a Wikihow (starting at method 2) about ribbon and bows:

Decorate a Wedding Car with Ribbon