Tough questions. I'm going to jump in here because nobody else has. I have dual uk and Canadian citizenship and I have spent time in both locations, but I am single. So I haven't had exactly the same issues as you but I am somewhat familiar with the issues. No clear solutions though.
Are you planning on going back and forth or spend time mainly in one country? Not moving repeatedly is the best way to avoid taxation issues but that makes life Less interesting.
The issues of differing rates of inflation and return, and currency fluctuation are obviously an issue. I would suggest normally that you invest equities in a third currency that is relatively stable, and transfer funds to the country you are currently in. In the past I have invested in japanese stocks and bonds, but right now the yen is not a good safe haven (IMHO). Everyone has an opinion about the next best thing (gold, renminbi, hkd, etc.) but I have no crystal ball so if you come up with something, let me know.
Do you file jointly or separately? You may be able to easily avoid double taxation by filing separately. I.e. One of you in canada, and one in the UK.
Each of you should purchase a primary residence in each country. Live in one, rent the other out when you're not there. Make sure it is a low maintenance property and you set up contingencies in place for emergencies. canada (particularly Toronto) isn't great for this right now, butit should be a long term goal.
I would also recommend Investing in some dividend bearing stocks in both markets. I stuck to large multinationals. Most of these get favorable tax treatment for their dividends if they have a Canadian or uk subsidiary. This may make them better from a tax point of view than etf's if you don't know where you'll be and dont want to rebalance your portfolio when you move. Limit your trades to avoid triggering capital gains. Use the dividend income to pay for trips in each location if travel is frequent. Keep a backup fund in each major currency to avoid losing money each currency transaction.
Look into major purchase costs in each currency, especially flights and electronics. There are often opportunities for selective purchases from the cheaper location.
Limit travel costs (easier said than done) and take advantage of frequent Flyer plans.
Max out the rrsp/tfsa options before you do any of the above.
Hope this has been helpful.