This largely depends on your BGP edge design and whether or not the peers are fully meshed inside your AS. If the routes learned from your upstreams are only present at the border routers then you'll need aggregate routes injected form the border routers to draw traffic towards one of those peers.
An example. Apple Computers uses 22.214.171.124/8 , if you want traffic destined for Apple to traverse a specific upstream, then you can advertise a 126.96.36.199/8 summary into your network with a local preference assigned to the BGP border router you want it to go to.
Obviously you can't do this for every BGP prefix, but identifying large IP blocks for webscale companies like Apple, Facebook, Google, YouTube, etc and advertising aggregates or leaking specific routes into the interior of your network can help to balance traffic across the different speed upstreams.
BGP Communities if they are available from your upstream can be used to help manage traffic inbound to your AS and achieve some load balancing. Check woth your provider to see what options you have to set local preference within your provider's AS and prioritize or de-prioritize your prefix advertisements within the upstream provider's AS.
Another option is to use software like Noction to help manage advertisements dynamically and detect packet loss and congestion. There is a free version that works with MikroTik.
Finally, as this is a very complex topic, if you want professional help with designing this, we'd be happy to help and work on this kind of solution every day. Visit https://iparchitechs.com/services/consu ... onsulting/
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