The establishing aerial view of Haplin, Minnesota ("Happy Town") is actually
an aerial view of the town of Port Hope, in Ontario, Canada.

The camera is looking northwest from the intersection of Walton Street & Mill Street

If you can handle Google Earth, here's a matching 3-D aerial view.

As the pilot episode begins, we see young Henley Boone arriving in Haplin, at a train station.

That scene was filmed at the old Uxbridge Train Station, built in 1904,
on Railway Street (at Spruce Street), in Uxbridge, Ontario.

That's about 30 miles northwest of Port Hope.

Here is a Google StreetView panorama of the train station:

As Henley and the real estate woman head into town, they pass the
"Welcome to Haplin" sign, which is next to a cemetery.

They erected that fake sign on the east side of Toronto Road, in Port Hope,
outside the St. John's Cemetery, at approximately 114 Toronto Road.

(The camera is looking southeast.)

Here is a Google StreetView panorama of the road:

 

When Henley and the real estate woman drive into town, we see Haplin's Main Street.

Not surprisingly, this is actually the main street of Port Hope: Walton Street.

In the photo above, we are looking east down Walton Street, from around 135 Walton.

Here is a Google StreetView panorama of the Walton Street, looking west:

They make a right turn, and that takes us from Walton Street onto westbound Queen Street.
That theatre marquee on the right side is the Capitol Arts Theatre, at 19 Queen St.

Here is a Google StreetView panorama of Queen Street

They then pass a church with that odd question mark/halo logo spray-painted on the wall.

They cheated a bit here, since that church is not really on Queen Street.
That church is actually St. Paul's Presbyterian Church, at 131 Walton Street. in Port Hope.

Here is a Google StreetView panorama of the church: