Treat yourself to some basic Shimano SPD shoes. Consider getting the pedals too. A popular entry model shoe is the M087 model, shown here with a basic SPD pedal:
The Shimano shoes are reasonably wide, the sizes are as per your trainer size, available in EU size increments. The M087 has a ratchet mechanism for doing them up, you can adjust this whilst you ride (which you cannot do with lace up shoes).
Note that most Shimano shoes did not require any vegans to be killed for their manufacture.
We have already worked out what is wrong with the Merrell product: sole not suited to cycling as it will bend. The sole will also get 'eaten' by the back of the pedal leading to the shoe not lasting very long. By contrast, the Shimano SPD shoe will last two years even if worn 18 hours a day with lots of walking.
Visit your local bike shop if you are pressed for time and see what they have got. You will be able to get the right size that way, particularly if you go in the afternoon when your feet have padded out a bit from you being on them all day.
Many shops carry the basic Shimano MT42 models with laces in a selection of sizes: these are very good and better suited to toeclips/straps than the velcro enclosure you get on the M087. Rarer but worth looking out for are the MT66 Shimano sandals. They are cycle-tourist-friendly.
If the shop carry the affordable Specialized shoes then do consider them as well - they are with the prerequisite stiff sole and 'lace-lock' to keep laces out the chainset.
If you do not find your size in your preferred shoe, do ask the shop about ordering 'special order', they can get them in for you quite quickly although when did 'this weekend' begin??? Maybe you might need to phone around a few stores or limit your choice to what there is in your shoes size.
If you end up forking out more money than you would have done on the Merrell sneaker, don't worry, you will forget about the outlay once you have put a few miles into the shoes. With the stiff sole you will be able to go at least 10% quicker/further, such is the efficiency saving of having stiff soled cycling shoes. That efficiency is still there if you don't get the SPD pedals, which you may want to look into after your tour.
You may also want to see what has been recommended on this question: SPD shoes that look like normal shoes