Hi Bill,

As you know spur-bearing apples are recommended for espalier. You should select a tree that’s hardy to zone 4B or 5A. 

While Golden Russet is hardy here, there's conflicting information online about whether this old variety is tip-bearing or spur-bearing. You might want to go with Honeygold instead. Most modern apples are spur-bearing.

Buying trees on dwarf rootstock would make it much easier to maintain your trees as they mature. Here's more information on rootstock choices. Note that "dwarf" apples may get ten to 12 feet high.

https://apples.extension.org/understanding-apple-tree-size-dwarf-semi-dwarf-and-standard/

The Chicago Botanic Garden recommends these varieties for espalier in the Midwest. The last three are University of Minnesota introductions:

“Popular varieties hardy to the Chicago area include 'Northern Spy', 'Golden Delicious', 'Liberty', 'Redcourt', and 'Holiday'. Others that have shown extreme hardiness and good disease resistance include 'Honeycrisp', 'Sweet Sixteen', and 'State Fair'.”

This page has a list of spur-bearing trees that are used for espalier:

https://thefruitgrove.com/50-apple-varieties-for-espalier-how-to-choose-the-right-one/

This is a good guide to establishing espaliered trees:

https://www.starkbros.com/growing-guide/article/espalier-fruit-trees

If you have an apple orchard nearby you're unlikely to need any new pollinating trees. But if you want to play it safe and add a pollinator, white-flowered crabapples with single flowers are a good bet. This page is helpful:

https://treefruit.wsu.edu/web-article/apple-pollination/

There is no way to identify apples in the orchard without doing a DNA test. Your best bet is to take photos of the fruit, note when they mature and compare to this list of apples that were developed by the University of Minnesota:

https://mnhardy.umn.edu/apples/varieties

Good luck with your exciting project:

You’re welcome!