Honestly, it depends. Youth development is an easy answer for countries like USA and second tier European countries that are already big on football, but any useful answer has to address that different countries are weak for different reasons.

You mention Canada and Bolivia, which are in very different situations. Canada's problem is partly cultural: football just isn't the biggest sport and at best it will always have to compete with hockey for national attention and participation. Bolivia probably has issues related to economic development that stymie growth and have seen it fall behind its neighbors, but otherwise culturally football is the top sport.

Even then these two are not by any means near the "weakest" national football teams. These usually fall under three deficiencies (or a mix of them): disinterest, people and economic resources. There are plenty of weaker teams whose fundamental deficiencies lie in national disinterest in soccer (or sports in general), which could be said of a lot of Asian countries. A lot of the weaker teams might be primarily football-loving countries, but are limited by a small (<1M person) population and would have to develop a highly efficient youth development system to even begin to compete. Furthermore, a lot of countries might have the population and interest in soccer, but are highly limited by poor economic development that prevents them from having a functional league, effective FA and generally speaking having the resources to train professional level footballers. You have to go 30 countries up from the poorest countries in the world before you start seeing World Cup teams like Ivory Coast and Cameroon, and even then that is thanks to African countries having close relationships with their former colonizing European power. You have to go up to #135 Honduras before you find a poor country outside of Africa that has developed a functional league and youth development system that can take it to the World Cup.