What cities or towns in the US or Canada that can theoretically survive an ISOT?

Most likely any pre-electric city (1890s or before) could survive ISOT, since the people aren't reliant on electricity yet. After electricity, a city would need to have its own power station supplying its own power to survive. An entire country would stand a better chance, or perhaps Texas, since it has its own grid.

Looking at the largest US and/or Canadian city (both by size and population) which would have the best chance of theoretically surviving an ISOT event, I'd nominate Houston and Oklahoma City. Houston, by courtesy of factors such as hosting the largest concentration of petrochemical manufacturing in the world, including for synthetic rubber, insecticides, and fertilizers, as well as being the world's leading center for oilfield equipment construction, and having the busiest port in the U.S. in terms of foreign tonnage, second-busiest in the U.S. in terms of overall tonnage, sixth-largest and sixteenth-busiest in the world; there'll be plenty of stuff, originally shipped into the Port of Houston with the intention of being imported or exported, for the ISOTed population to add to their stocks. Also hosts the Texas Medical Center, which describes itself as containing the world's largest concentration of research and healthcare institutions, with a strong healthcare industry in the city, and an agricultural industry which still exists. And as a minority-majority city, even in the event of a paleolithic ISOT, there should be plenty of genetic diversity in the founder population that'd result from the ISOT event.

Oklahoma City, though, while being situated inland (making the establishment of transportation and shipping links with the wider world they've been ISOTed to significantly harder), also produces a larges surplus of oil, natural gas, petrochemical manufactured produce, and other related goods and industries. And its agricultural industry, and agricultural output, is greater still- with a sizable surplus of food production within the boundaries of the city. Which, let's not forget, are extremely sizable- being a similar size to Houston (c.1,610 vs 1,625 sq.km in total), but has a markedly smaller population- estimated at 662,314 people last year, with a population density of only 417/km2. This is due to its urbanized zone covering roughly 244 square miles (630 sq.km), whilst the remainder of the area within the city limits (c.980 sq.km, 60.8% of the total city area) consists of rural watershed areas incorporated by the city, dominated by farmland and oilfields. As such, drawing comparisons, if we were talking about Oklahoma City as a nation, it'd be the 171st largest by area in the world, just behind the Comoros and significantly ahead of São Tomé and Príncipe (also being larger than the Faroe Islands); and it'd be the 163rd largest by population, behind the Solomon Islands (and Macau) and ahead of Luxembourg.

It'd also only rank in the 30's on the list of the most densely populated country/dependencies in the world, with a population density lower than those of such countries as Bangladesh, Taiwan, Mauritius, South Korea, Rwanda, The Netherlands, Israel, Haiti and India. Even within the Oklahoma City limits, its agricultural land area as a percentage of its total land area is significantly higher than the world average (of 36-37%); and the degree of urbanization by area within the boundaries of the incorporated city, of 39.18%, is only slightly greater than that of The Netherlands (36.58% urbanized), and actually significantly less than that of Belgium (44.88% urbanized). It's also a markedly a larger net exporter of food (and oil, and gas, and electricity, and fresh water), on a per-capita basis, than any of these nations. As such, Oklahoma City's chances of surviving such a time-travel ISOT event should be considered to be on a par with, or slightly better than, those of Japan, the Philippines, Sri Lanka, the Netherlands, Belgium, El Salvador, Puerto Rico, Réunion, Martinique, Curaçao or Grenada.

I would say that while Houston and Oklahoma City would likely survive, I feel like if you take the Dallas-Fort Worth Metropolitan area (Denton, Collin, Dallas, and Tarrant Counties) you'd be able to survive in basics because 1, medicine and manufacturing would, to a degree, survive, and 2, agriculture would survive. Further, I think that really in general Texas (and Oklahoma as an extension of Texas) would be BEST suited of all US States to survive an ISOT, because one Texas is generally self-sufficient and two the sheer diversity of the states accounts for most needs. I feel like Hawaii and Alaska, due to there isolation, could likely survive. I hesistate to say California because California may be too diverse and not culturally or politically adhesive and this could lead to infighting, while Texas shares a common culture, spirit and hertiage, which is key to the independent survival of a state.