Swissinfo.ch had an overview on countries with DTA, and if tax on 2nd & 3rd pillar can be claimed back. If their information is correct (I have personally no idea), in Canada you cannot, in US you can, in Mexico you can claim it back on 2nd pillar but not from 3rd pillar.
If it is covered by a DTA, it essentially allows transfer of money to the destination and pay tax there without having to pay tax in the origin country as well, respectively the ability of claiming tax back from the origin country once proof is given that the destination country is aware of the money’s arrival. If then more or less tax is paid in the destination country is a different matter altogether and not a concern of the origin country anymore.
The question now would therefore be which countries have a DTA with Switzerland, if the DTA covers 2nd and/or 3rd pillar, and if that country then has a lower tax on it. There is talk in some expat forums that 2nd pillar tax was successfully claimed back after emigrating to Thailand, and no tax had to be paid according to the Thai tax code. The CH-Thailand DTA does not cover 3a however. Here is a link to a Swiss lawyer based in Thailand that could advise on this.
I personally do not plan on this, because a) who knows if this is still possible by the time I get to FIRE, b) financial planning that actually needs this to work would be imprudent and c) it is a lot of hassle with my family situation to just get around some tax money. At best it would be a welcome windfall if it / something like it would work out, but I’m not planning for it. If you are single and close to FIRE however, this might well finance 1-2 years of living expenses in Thailand if that is your thing and you have significant 2nd pillar capital.