The simplest way in home / Small office is to connect your two WAN point by a router, and router to the LAN.
Things need to be take care:
1. IGRP / EIGRP should be adopted if your two ADSL have unequal speed (Since only these two support unequal cost load balancing)
2. When you connect LAN segements together, better ensure no switching loop, or otherwise enable STP.
3. Take care when you config your edge router. If static routes are used, make use of polic routing to avoid possible link down.
More advance technology such as GLBP can be used to solve the problem
VPN is definitely resource consuming unless you got dedicated VPN concentrator/firewall.
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