If such iconic landscapes as the Great Lakes, the Mississippi Basin and New York Harbor are proof of anything, it's that the North America we know has been shaped by ice ages coming and going and coming back again in the last two-and-a-half million years of Earth's history.
What sorts of geographical differences within Western North America (from Nebraska to the Pacific coast) would I expect to see if the ice ages have been lasting for 14 million years instead of two-and-a-half?
Glaciers, which are basically small versions of ice sheets, have been known to carve out mountains and make sharp valleys.
Ice sheets are essentially giant glaciers, that are moving extremely slowly due to their huge mass. But due to their sheer mass, they exert tremendous amounts of pressure on the crust. When the ice sheet melts, the crust bounces back up, creating weak spots.
The best example of this is the Sturtian Glaciation, demonstrated in this video- National Geographic documentary, jump to the moment at 28:36. As the ice sheet melts away, the crust bounces up, creating weak spots in the crust, where mantle material (magma) can penetrate, creating more volcanoes. These volcanoes induced more greenhouse gases like CO2, SO2 into the atmosphere, causing the ice sheet to melt even more and cause the crust to bounce up even more, being stuck in a self-destructing feedback loop. Bonus point is that the Sturtian Glaciation lasted for 15 million years, close to your "14 million year" duration.
TL;DR You would have pointy mountains, sharper landscapes, and a lot of volcanoes
You would get a mix between eroded mountains, larger areas of deposited materials and sharp pointy mountains. If you look at the different nature between north and south of Norway, where the glaciers were present much longer in the northern and inland parts, you will get a small glance into the difference. Along the western coast of Norway, where the ice receded first, you get deep valleys, "bowl" mountain valleys, rounded mountains that were under the ice and had been "scrubbed" by the ice, and tall, sharp and pointy mountains that were tall enough to emerge over the glaciers surface.
In northern parts of Norway the land is much flatter and have large areas of sediment deposits. [edit]Along the coast where the ice receded early (because of the warming from the gulf stream) the mountains are sharp and steep, but around the mountains the land is flat. This is because of changing sea levels (simplified). In other areas you can clearly see the scars in the rocks from the ice scrubbing them, leaving long, narrow, furrows in the direction of travel. These again created long, narrow islands in some areas.
Some places have large boulders that have been carried by the ice to seemingly impossible places. In some areas ice have been grown over and since melted and collapsed, creating deep lakes with overhanging or vertical edges (some of them have not collapsed yet and can be quite dangerous).
Just imagine everything more severe. All the mass worn from the mountain formations would get transported, dammed up, piled up and otherwise moved around by water and ice to be deposited "down stream" or into the oceans (ice is technically fluid... it just flows so slowly it is perceived as solid). The process of the glaciers melting would also create river valleys, lakes, "bowls" where water dammed up and, in many cases, broke through one side and flooded out creating an opening. Also take a look at the south pole and Greenland.
[edit] In addition, as mentioned by Furious Arcturus, the weight of the ice would create pressure on the continental plate, changing the coastal line.
As the ice presses down on the tectonic plate, it will develop faults where volcanos occur. This will aid in the process of ice melting. The melting ice will then make the sea levels rise, eroding the coastline and creating sediment deposits. After a while the edges of the tectonic plate will start to rise, thus raising the land, leaving planes of sediment behind. Then more water will melt, sea levels rise and the water digs into the sediments left behind by the land rising, then the land rise and water recedes in a circle of regressions and transgressions.
This process can be easily be seen in areas of Norway where you have the Tapes transgression shelf, a sedimentary shelf that is flat on the top with a sharp drop down towards the sea. In some areas this is as high as 20 to 30 meters above todays sea level with the marine maximum (the highest the water have been) at 60 meters.
This process is still in effect today. The tectonic plate where Scandinavia is situated, is still rising, making the British Isles (placed on the outer edge of the tectonic plate) sink. In addition you can take a look at Iceland to see the effect of glaciers, tectonic plate movement and volcanos in relation to each other.
