what are the deployment scenarios for L2TP tunnel, GRE tunnel and MPLS Tunnel (l2vpn vpws)
I'm reluctant to answer this question because there are exceptions to just about any scenario. But here goes anyway. Generally speaking:
MPLS is commonly used when you want to isolate the data paths over a shared network infrastructure. MPLS allows for separate routing/forwarding for each isolated path. The most common scenario is a carrier offering private WAN connectivity to its customers.
L2TP is an older technology that's rapidly becoming obsolete. It is (was) used to provide layer 2 connectivity over a layer 3 network. VXLAN is probably the best replacement.
GRE, as the name implies, is a generic tunnel that can be used for L2 and L3 routing over a L3 network. A common use case is routing between sites when you don't have control over the intermediate network.