In a given Ethernet frame containing the HTTP GET message can we tell apart wether the mac address of the destimation is of a router or end host?
Not by the frame alone. However, if the destination IP address is local to the capturing host (=located within the same subnet) then the MAC address is that of the destination host. Destinations outside the host's local subnet require a router, so the destination MAC address will be that of the appropriate gateway.
If you've captured the frame through mirroring/SPAN please replace "capturing host" with "capturing port".
Of course, you can also use the MAC's OUI to make an educated guess which kind node is addressed. Many vendors build different device types though, so you might not be able to distinguish them.
EDIT: When examining a full (or rather lengthy) trace, you can also guess based on the ARP (or NDP) exchanges. Packets destined for local nodes and gateways require a previous ARP for the destination IP. Packets destined for remote nodes are encapsulated by MAC frames targeted for one of the gateways and there's no previous ARP for the destination IP itself. However, this is also possible using multiple IP subnets within the same L2 segment together with static ARP entries - not too common but possible.