Ordering flowers online is not much different than ordering flowers directly from the local florist. Florists made arrangements with each other years ago. If you ordered a bouquet of flowers to be delivered to your grandmother on her birthday from your local florist, that local florist would call the florist in the area closest to your grandmother's house to make the floral arrangement and the delivery. The same thing happens when you order flowers online. The online florist will make the floral arrangements through the florist in your area who will also deliver them to the location you have specified.
You don't have to worry about them going through the postal system or UPS. FedEx doesn't even deliver the floral arrangements for you. You will have the flowers you ordered brought fresh and to the door by the local florist who has been contacted by the online florist. When florist first started working with each other around the country and possibly even around the world, they started with the FTD florists. Times have changed, but the way florist work together to make fresh flower deliveries has not. They have had this practice in place for over 100 years and they do it well.
So now you don't have to worry about where the florist is located when ordering flowers to be delivered. The florist can be in Burlington, Ontario, but you will still receive a fresh bouquet of the flowers you ordered at your door.