Hi beentherebefore and welcome to the forums!
You can use either MLT or LACP to group multiple links between your core and edge switches. I would strongly suggest you use MLT between Nortel/Avaya switches.
You can also do a DMLT (Distributed MultiLink Trunk) where you use ports on different switches within a stack to add additional redundancy.
If you are looking for high availability then you will most certainly want to look into SMLT although I don't believe SMLT is available on the ERS 4500 series switches. I believe you need to be using the ERS 5500/5600 series switches with the Advanced Routing license.
As an example, just using a stack configuration - no SMLT you can use DMLT. Create MLT 1 and add ports 1/1 and 2/1 to the MLT on the core switch, you could connect those to 1/47 and 1/48 on the edge switch if you are using a single switch or you could use 1/48 and 2/48 if you have two switches stacked together as your edge switch. Just make sure you set the ports to TagAll and then add the VLANs you want to extend across the uplinks/downlinks.
Good Luck!
