Well, that's really not true. The four densest states are wealthy Monaco, Macao, Singapore and Hong Kong, and "Among 88 countries/territories having population of over 10 million, Bangladesh (1278) is most densely populated followed by Taiwan (669), Republic of Korea (526), Rwanda (507) and Netherlands (507)". Only Rwanda is in the bottom half of the world's poorest countries.
I won't belabour the point, but there's absolutely no way Australia or Canada, even just focussing on "small" hospitable areas, would be anywhere close to wiping out nature if they increased their populations. Even the "populated" areas of eastern Australian and southern Canadian generally only have 5-20 people per square km, it seems. We're talking about enormous amounts of land. England is pretty red on that density map, yet you can drive along the motorway for ages seeing nothing but open land and occasional villages. So yeah, not buying it I'm afraid.