The protocol you need to use for that is the Border Gateway Protocol, or BGP. You’ll need at least a /24 (class C) address space from each provider. ISP’s don’t forward BGP for smaller address ranges than that. Normally, one ISP is the primary and the other is the backup. While it’s possible to propogate multiple routes to load balance inbound traffic, outbound is usually router to one ISP or the other, not both. You can only have one default route. Setting up BGP is not trivial and I’d recommend that you consult with a network professional to set it up, interface to the ISP’s and document it all for you.
To get load balancing to happen, you need equal cost routes pointing to the interfaces involved in the load balancing. For example, on Router A load balancing 2 T1’s, the show ip route output might include something like this:
S* 0.0.0.0/0 is directly connected, Serial0/1
is directly connected, Serial0/0
And on Router B the show ip route output might include something like this:
ip route 192.168.8.0 255.255.255.0 Serial1/3 10
ip route 192.168.8.0 255.255.255.0 Serial1/0 10