I am assuming that the DSL Providers are giving you some sort of DSL Modem handing off ethernet to you so you would plug both of them into the 2 fixed WAN Ports on a 2811 and a 2811 has 8 ports for a managed switch so it would be a good fit for your situation. Failover is a little tricky when it comes to NAT'ing properly but it can be accomplished both inbound and outbound. You would also have to setup a secondary MX record for inbound MAIL redundancy.
One problem you have to overcome is that the if one ISP Goes down the ethernet of the DSL modem will probably remain up so you might have to do some sort of SLA Monitoring with Object Tracking to look past the DSL Modem to monitor connectivity and change the route to the secondary ISP if needed using weighted static routes.
Now load balancing is a whole other ball game. The only real way I know to do it is to connect DSL directly into a router with DSL Router Modules and run PPP or IP packet load sharing but you have to connect to the same ISP and probably the same router at the same ISP so I am not sure that is going to work for you.
With all that said I have had some customers look at what it would take configuration-wise to get all of this done and a few of them have gone with something like a Symantec Firewall 200 series with High Availabilty and Failover which is much easier for them to configure or a product made by FatPipe that is made for larger deployments and larger bandwidths.
