Hi you can have multiple exit points with eigrp as it supports equal cost and unequal cost load balancing but if you only want 1 ISP link active at a time use hsrp between the routers
is this just a lab as you would usually have BGP on your wan with eigrp redistributed into it
http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3560/software/release/12-2_52_se/configuration/guide/3560scg/swhsrp.html