"Controlling these cold lands is of vital importance to gain full control of the Northern mountains and to block the way for the infected from beyond the mountain range. Our scouts have detected an Infected Giant. These creatures have grown beyond imagination by some unknown effect of the infection as if it were a mutation. Your goal is to take the Giant that roams the Northeast down and get rid of all infected in the region. You must be extremely cautious with the Giant. It will be your ruin if you attract it to the colony before having a great army."
There's a fair amount of bad news on Lands of the Giant. Being a winter map, it will take more energy and thus more mills to power buildings. There's also a lot of open space to deal with, precious little of which is viable for farming, making securing your entrances difficult, and the only easily available Iron deposit is a long way from the base, at the mouth of the canyons that lead to the Giant. Good news is that this map doesn't have swarms (mini-swarm will still spawn).
DO NOT UNDERESTIMATE THE GIANT. He is very much as dangerous as advertised, with 10,000 health and a 30% damage reduction. A lone Soldier would have to shoot him over 900 times to kill him, and he can crush your base single-handedly if you let him. However, Giants are also deaf -- unlike every other Infected, the Giant will only aggro if he sees you or being attacked. So just stay away from him until you're ready -- he may wander outside of his starting pocket but won't go very far.
The Lands of the Giant will rush you in figuring out how to kill this thing. There is a time limit of 77 days, but it doesnt have set swarm waves to handle. This does not mean no offmap infected to deal with, and indeed a fairly significant number will come at you with no fanfare, but it is overall more manageable. It being cold, all Infected also move slower and are less aggressive overall.
The strategy, thus, is to first clear out the area immediately around your CC, focusing on three intercardinals -- northwest and southeast, to reach chokepoints you can wall up against the offmap Infected, and northeast, to reach the iron deposit. All three of these are quite a ways from your CC, with the best northwest chokepoint being almost at the map edge, so remain on alert and keep an eye on your minimap. It's very easy for Infected to sneak around or lurk in the corners on this map, especially since the power requirements, scarce farmland, and lack of time limit can encourage expanding more rapidly. Be careful and thorough.
If you should accidentally aggro the Giant, or if he blunders into your workings before you're ready, KEEP HIM AWAY FROM THE COMMAND CENTER AT ALL COSTS. This includes demolishing buildings in his line of advance to keep him from noticing the rest of your base, though that should be a last resort. Your best bet is to have a unit or, more likely, group of units, try to lure him off into the northern reaches of the map. While this will likely cost you those units, you need to make sure he doesn't get chained into your base.
Your best bet for actually killing the Giant is to set up a meat grinder and drag him into it. Pick one of the approaches to his lair -- the one with the iron deposit works well -- and pack it to the gills with walls and towers, loaded with Soldiers and Snipers. Rangers are to be avoided in this -- they just can't put out the damage needed to put something this big and tough down, and their low-impact combat has no relevance considering the Giant is deaf. A "deathsquad" of Soldiers can clear the map and gain Veterancy, while backing up your towers later. Once you've cleared out the rest of the map and prepared your trap to your liking, send someone over to get the Giant's attention and drag him into your meatgrinder. THIS is actually a job much better suited to the Ranger, as the Giant is shockingly quick for his size and can outpace a Soldier. Once baited, hit the Giant with everything you've got, preserving your units as much as possible. He's big and very, very tough, but he's not invincible.