Quote 1
BEN [chuckling]: So this is Brooklyn, eh?
[…]
BEN: Opportunity is tremendous in Alaska, William. Surprised you’re not up there. (Act 1)
The American West is portrayed as a land of opportunity waiting to be tapped. Willy is haunted by the fact that he didn't accompany his brother to Alaska. It seems like sometimes he feels that this missed opportunity is the thing that robbed him of a chance at the American Dream.
Quote 2
BEN: You’ve got a new continent at your doorstep, William. Get out of these cities, they’re full of talk and time payments and courts of law. Screw on your fists and you can fight for a fortune up there. (Act 2)
The American West is depicted as rife with opportunity and prosperity, an ideal place to pursue the American Dream. In a way, it's a much more basic version of the same dream that Willy is following. In the West, however, the fight is man vs. man and man vs. nature.
Quote 3
LINDA: You’re doing well enough, Willy!
BEN [to Linda]: Enough for what, my dear?
LINDA [frightened of Ben and angry at him]: Don’t say those things to him! Enough to be happy right here, right now. [To Willy, while Ben laughs] Why must everybody conquer the world? You’re well liked and the boys love you and someday—[to Ben]—why, old man Wagner told him just the other day that if he keeps it up he’ll be a member of the firm, didn’t he, Willy? (Act 2)
Linda expresses concern that Willy's massive aspirations are getting the better of him. She seems afraid that if Willy latches on to his brother's big dreams of success, then she may never see her husband again.