Dual WAN - ideas?

I have a plusnet FTTC connection running at 15/2 (cab is miles away), I also have a EE 4G connection running at 60/30.
Any ideas on the best hardware to achieve a bonded setup (or as close as I can get)
I want certain Mac addresses to default to a particular WAN interface.

Current setup
Bt line > open reach modem > plusnet cheap router

4G Ethernet router.

Currently I just switch between wifi networks but that's a pain and my wifi printer won't work on the 4G router.

I think this is the TP Link router/load balancer a few people have mentioned in the past.

Load balancing is not bonding per-se but usually achieves what people want. Bonding gives you one single faster connection, balancing means no one use will go faster, but when doing multiple things the load is spread around.

I am currently very happy with the performance of my Zyxel SBG3300 N on my FTTC line. It has squeezed a couple more MB/s out of my line compared to the HG612 modem. I also connect to a wireless Canon printer.

http://www.zyxel.com/uk/en/products_services/sbg3300...

It caters for load balancing between ADSL/VDSL - WAN - 3G Dongle though I have no experience in setting it up in this mode. Check out the compatible 3G dongle list before purchasing.

You often see them on Ebay for around £90 second-hand but unused.