QoS-ish question / Upload

I am looking for suggestions on prioritizing traffic.

I recently signed up for BackBlaze and I am in the process of syncing 10TB of data to their cloud.

When I am doing this the upload of my primary connection is fully saturated, which ultimately affects other traffic - even that which is only download traffic.

My goal is something like this:

If traffic does NOT equal Backblaze - give it priority.
If traffic IS BackBlaze, allow it to use ALL bandwidth when no other priority traffic exists.

The goal being to allow Backblaze to upload at “full speed” and also ensure that other traffic is “first” within the queue.

Backblaze can be identified by the target URL. It does not have it’s own protocol or port number.

Additional context about my setup:

I have 3 WANS.
1Gb/35Mb - cable modem
50Mb/1Mb - DSL
35Mb/5Mb - WISP

I currently have outbound policy sending all Backblaze traffic via cable modem-only.