Expand Column Array List

As a rule of thumb, any transformations should be done as early in the process as possible, so if it can be done in SQL you may still consider that as the first alternative.

It can be done in the Query Editor by adding columns using text between delimiter functionality, if the structure is the same for each field.

let
    Source = #table(type table[Column = text],
        {{"@{city=Stratford; state=ON; country=Canada}"},
         {"@{city=Boucherville; state=QC; country=Canada}"},
         {"@{city=Elora; state=ON; country=Canada}"}}),
    #"Inserted city" = Table.AddColumn(Source, "city", each Text.BetweenDelimiters([Column], "=", ";", 0, 0), type text),
    #"Inserted state" = Table.AddColumn(#"Inserted city", "state", each Text.BetweenDelimiters([Column], "=", ";", 1, 0), type text),
    #"Inserted country" = Table.AddColumn(#"Inserted state", "country", each Text.BetweenDelimiters([Column], "=", "}", 2, 0), type text),
    #"Removed Columns" = Table.RemoveColumns(#"Inserted country",{"Column"})
in
    #"Removed Columns"

This is how the insertion of column "country" looks like in the Query Editor (I forgot to highlight "Extract" in the middle of the ribbon: that's where you can find "Betweeen Delimiters"):

I adjusted the column name and the step name after each column insertion.

Dynamic alternative:

Much more fun (and much more dynamic) is to transform the texts to record format, transform these into actual records, transform each record in a table (each with 1 row) and then combine all tables to 1 table.

Otherwise it requires some query editing in the advanced editor.

Just to illustrate the dynamics, I added a field helper to 1 of the rows,

let
    ReplacementList = {
        {"@{","["},
        {"=","="""},
        {";",""","},
        {"}","""]"}},

    Source = #table(type table[Column = text],
        {{"@{city=Stratford; state=ON; country=Canada; helper=MarcelBeug}"},
         {"@{city=Boucherville; state=QC; country=Canada}"},
         {"@{city=Elora; state=ON; country=Canada}"}}),

    ReplacedValues = List.Accumulate(ReplacementList,Source,(t,r) => Table.ReplaceValue(t,r{0},r{1},Replacer.ReplaceText,{"Column"})),
    TextToRecords = Table.TransformColumns(ReplacedValues,{{"Column", Expression.Evaluate, type record}}),
    RecordsToTables = Table.TransformColumns(TextToRecords,{{"Column", each Table.FromRecords({_}), type table}}),
    TablesToTable = Table.Combine(RecordsToTables[Column])
in
    TablesToTable