Do you have you own AS for your /29 and /48 ?
Are you natting at this point ?
Are you running GRE with the same router you have the directly connected BGP session to ?
Sharing the load will probably be difficult if you are gonna source your traffic from the same addresses on both routers as you can't guarantee return traffic will return to the router that forwards you initial session. It all depends on how your ISP is routing your addresses to your routers though. If you split up your /29 into /32 and assign your external addresses (you can use an RFC1918 address for this if your ISP allows it, they might not wanna fiddle with their VRF for internet to prevent an RFC1918 address being advertised in their routing table) to the routers and make your ISP route each of the /32 to your routers.
You can maybe also be able to advertise your different /32 for each routers with different Local Preferences to force traffic to the different routers. (This would be prefered solution)
It really depends on how far your ISP can go.
With VRRP you'll be able to load balance per VLAN only, but make it redundant also.
You'll be able to use route rules to send their traffic to each router based on their source address.
Does it make kinda sense : P ?
Thanks for the answer. This is an internal AS for now so the ISP above take care about advertising it on the net.
If I read you you’re suggesting to split the prefixes between the 2 groups? and ensure the subprefixes goes out by a 1 router at a time so the ISP can eventually merge them?
I don’t expect to do NAT at this level. The routers will be just here to pass the data. Originally I was thinking each machines begind a router could advertise its own ip. The real goal of it is to prevent teh case one remote dc or a link to it is down. Do you have any configuration to share, that would be very helpful .