How to resize images before uploading directly to s3

I'm using Ember on the frontend and Node/Express on the back end. I've got image uploading directly from my client to S3. My issue now is that the image sizes are huge (970 × 728 pixels (Natural: 3264 × 2448 pixels)) and I want to optimize the size. I've been able to do that using the canvas. But the resulting dataURI is also, very, very large. I could store it on my server, but that seems silly since then I'll have 1 large file sitting in s3 and another sitting in my server for every single image. I feel like the solution should be to upload the dataURI (in blob form) directly to s3 in the first place, but that's where I'm stumped. In order to draw the image in the canvas, I need the src url from s3. So how can I get the dataURI and save it to s3 without already having the original in s3 in the first place? Or should I be saving both versions in s3? Any advice on how to achieve this would be great. Thanks!