I'm not sure about your cable connection but if something similar to a Draytek Vigor 120 ADSL ethernet bridge modem exists for it, you could just build a linux box, stick 3 nics in it (one for each bridging modem and the third facing your internal network) and use that as your router.
You just bond the two public facing nics together with ifenslave, setup pppoe and write an iptables script.
Also, IIRC (been a while since I did it), normal bonding only gives you round robbin i.e. your max speed is limited to the bandwidth of whichever external link your connection is forwarded through at the time (unless you use an ISP that can do MLPPP - which is rare). If you want to combine the bandwidth of both connections into one fat virtual pipe, you could get a cheap VPS and then run an Open VPN link over the bonded virtual interface on your linux box at home to the VPS box (I think! I last played with this 4 yrs ago and details are hazy...).
You just bond the two public facing nics together with ifenslave, setup pppoe and write an iptables script.
Also, IIRC (been a while since I did it), normal bonding only gives you round robbin i.e. your max speed is limited to the bandwidth of whichever external link your connection is forwarded through at the time (unless you use an ISP that can do MLPPP - which is rare). If you want to combine the bandwidth of both connections into one fat virtual pipe, you could get a cheap VPS and then run an Open VPN link over the bonded virtual interface on your linux box at home to the VPS box (I think! I last played with this 4 yrs ago and details are hazy...).