Today, I attempted to see how far apart two places are by car using my GoogleMaps app. It was between 2 US locations, and I was offered $15 off my first Uber or Lyft (competitor in the States) ride by booking it through Googlemaps. In Canada, it's only $15 CDN off and only with Uber. Some report it expired in February, but I still got the offer today.
You first need to try GoogleMaps for 2 US locations. Then, the offer pops up. Then, switch it over to two Canadian locations. Even then, if it's not your first time using Uber, it still may only ask you to link all your private info of Uber, including your payment information, and then get stuck like it did for me.
No promo code seems to be required, though if you use "GOOGLE" as your promo code, it won't work if you've used Uber before, but through GoogleMaps it will work. Check to see if the offer pops up when you use GoogleMaps for directions.