Multiple site-to-site VPN connections between two networks

I have a client running a site-to-site VPN connection in order to allow secure RDP access to users at a remote site.  The remote users are on a completely separate Windows domain and use the tunnel purely for port 3389 access to virtual workstations and RDP servers at my client's site.  My client maintains two WAN connections - one from a DSL provider (on which the VPN tunnel lives), the other from a cable provider.  They each have their own separate static IP address blocks.  

My client uses a SonicWall TZ210 and utilitzes some of the bandwidth management features to optimize Internet traffic between their two WAN links.  What we don't have is a redundant VPN connection to the remote site.  The remote site apparently uses Cisco routers on their end which hasn't been any problem at all for the site-to-site VPN connection.

Is it practical to set up two VPN tunnels between the two sites so that if the DSL connection fails the cable connection can act as a failover?  Would the remote site also need two separate IP blocks on their end or can they do something akin to a one-to-many relationship?  Even if it is not practicle to have true failover capability, it would still be nice if I could uncheck the primary tunnel in the event of a DSL outage and instead mark the cable connection as the active tunnel.  Is this easy to do?