I didn't find it hard, tbh. Then again I got experience with the old PG to know how to plan for it.
My core panzergruppe at the time had
2 bridge units, 3 recon units, 2 arty units (I used a SPG and a towed one, but I find that towed ones are good enough by themselves), 2 engineer units, 4 armored units (All the best PzIII possible), one 88 flak, 3 fighters, 2 tac bombers, 1 strat bomber, the rest infantry.
Two battlegroups, one north, other south. Use your bridging units to cross rivers out of defended bridges (which are all in the map :P). as other says focus on the enemy air assets on first turns, otherwise your support units (and those travelling in trucks) are going to suffer a lot. Enemy armor (particularily T34s) are going to be a problem so focus your tac bombers and armor to deal with them as soon as spotted...and don't forget your 88 flaks in antitank mode will utterly smash any hard target you happen to have near at any given time.
Use your recon units (you have an extra one in the scenario, non-core but useful) to spot what's laying ahead of you in advance. Use them too to flank defended spots and get to the rear where they can really deal a lot of damage to enemy arty units (their consecutive movement rule helps a lot to maneouver through tight spots when needed).
always remember the principle of blitzkrieg: let enemy strong points (usually well backed infantry entrenched in cities or rough terrain) for your infantry, use your mechanized assets to push forward, get to the rear of those positions to deal with their arty/antiair, and to crush anything they find in the open. For the entrenched infantry use your arty/bombers to soft them somehow, then a direct attack by engineers (no rugged defence against those flametrhowers, buddy ;)), and then by other infantry units. They don't last long after that.
As for Brest others have said it before me: leave it alone and just bypass it. Use a bridging unit to the north to cross the river with the bulk of your panzergruppe and move forward, leaving one or two regular infantries back to deal with it. Once their arty is gone (should be your main goal in the first turns to get a pz unit besides it to crush it), is just a matter of hammering it with the gustav, will fall sooner or later.
The rest is just dealing with what comes your way. Some flexibility and some improvisation to deal with unexpected threats (which should be few - if you're using your recon units the way you should :P), and this scenario is easy to pull off :)
"Look at me! look at me!!!
Not like that! NOT LIKE THAT!!!"