This is a question with lots of answers .... assuming that you have multiple routers connecting to two different ISP's do you have a third master router that will be making the decisions about where to route? If so your client laptops can still use this device as its default gateway.
Lets assume that is the case, but even if you have two internet connections direct on your laptop the theory is the same.
you can split the traffic by destination IP (using route commands) so that all traffic to say your work IP range went to router A and all other traffic went to router B. You can increase the granularity with using IP + ports i.e. all web traffic to router A and all e-mail traffic to router B.
You need to read up on the "route" and "iptables" commands but it is entirely possible.