What is "the backstop"? I'm not sure where that terminology came from, but here is the point as I understand it.

Britain leaving the EU single market and customs union would, in principle, mean checkpoints along the 300-mile land border between Northern Ireland and the Irish Republic -- which has been "open" since the 1998 agreement ending the Troubles. These border checks would be required because the Irish Republic is staying in the EU, whereas Northern Ireland is part of GB and therefore will exit the EU with Brexit. As we learned in the John Oliver video, new border checks would theoretically be targets for Irish militants who want to reignite the Troubles.

The EU and Ireland suggest "the UK will follow many EU rules “unless and until” “alternative arrangements” ensure no hard border." But GB getting out from under these EU rules is the reason Brexit exists -- and they consider following EU rules post-Brexit an affront on their sovereignty.

"Britain says it will not impose border checks. So has Ireland. The EU says there must be checks on British goods coming in. A brief status quo on the border seems likely. But the EU will want to see at least discreet checks being made, rather as are envisaged under the “alternative arrangements”.

If not, Britain would have a “back door” to the EU single market and Ireland could risk having its own exports to the rest of the EU being subject to checks at EU ports to ensure they are not British." "... the EU says the backstop is a vital defense for its single market against a major economy (GB) dodging its rules."

We don't really have a North American equivalent, but this is a weak approximation. Assume Bacardi has made a deal with Mexico. They ship their rum to Mexico, and then it drives over the border into the US uninspected and untaxed.

Products going into the EU must comply with EU laws of production, and must be taxed. An unchecked border between Northern Ireland and the Irish Republic guarantees unregulated and untaxed foreign products flooding the EU markets.

All of my quoted material came from here.