Multiple Site to Site VPNs / dynamic vs. static routing

1) The tunnel won't come up until "interesting traffic" is sent out to the other side. There is a configurable timeout set for tunnels and if no traffic is sent for awhile the tunnle will drop. i'm niot sure about testing without dropping the link, but I would want to test it by dropping the primary link. It's the only way to be sure that it will work.

2)You say that the internal network is using MPLS. What are you using for your secondary links? DSL? T1?

Could you explain your network setup a little better. Are you setting up a full mesh between the sites, hub and spoke, etc..

Do the sites have internet access too? or just the MPLS?

Yes you would want to use a dynamic routing protocol. (Eigrp or even ospf) It can be done via static routes but you would need a route for all other sites/networks. With just 3 sites this isnt too bad to configure, but if you expect future groth/more sites, it may become difficult to manage. As each site is setup like this:
MPLS Cloud-------Inside Router-----(users on LAN)-----ASA-----------T1/DSL Router---------Internet
                             
Your inside router would normally route through the MPLS cloud because it's metric/weighting for those routes should be lower than the static/default route out to the ASA. When the router does a route lookup, it will match the destination address to the closest route in the routing table.  Basically a static route to the 1.1.1.0/24 network would match the address 1.1.1.5. Then if there are no closer routes, the default route would used. Point the default route of the Inside Router to the ASA and set a default route from ASA to the T1/DSL router.

So you will have 2 static routes on each MPLS router and a default route to the local ASA. Once the ASA recieves the packet it will  match "interesting traffic" based on your acl's and then send it through the tunnel. Since the clients will have the MPLS router set as their Default Gateway, any Internet bound traffic will hit the Inside Router, it wont have the route so it will forward it to it's default route (the ASA) and then the ASA will default route it to your T1/DSL router, which will send it out to the Internet.

That is the easiest way to make it work. I hope that helps you.