We found no Marqueur page that describes exporting a pool. Each pooler has a page there that lists their players: copy it, one pooler at a time.

The pooler pages on Marqueur

In your pool on Marqueur, open the STATS menu, then Classement (standings). Each pooler has their total there, in the TOT column.
Click a pooler's name. Their page lists their players in three tables, JOUEURS, DÉFENSEURS and GARDIENS (forwards, defensemen, goalies), with the NHL team abbreviation in front of each name.
Copy those tables into Excel or Google Sheets, then repeat for each pooler.
Arrange the columns: the pooler's name becomes pooler, the player's name becomes joueur and the abbreviation becomes equipe_lnh. For position, write F for the players in the JOUEURS table, D for defensemen and G for goalies.

Marqueur writes the round after the name, in parentheses: "Cale Makar (1)". Remove it, or Estrade won't find the player. In Excel, Find and Replace (*) with nothing does the whole column at once. Marqueur's abbreviations aren't always the NHL's (MON, CLB, WAS, LV, NJ or TB, for example). Estrade flags them without blocking; replace them with MTL, CBJ, WSH, VGK, NJD and TBL to avoid the warning.

The Estrade template

Estrade reads a five-column table, one row per owned player, with this header and in this order:

pooler,courriel,joueur,equipe_lnh,position

pooler: the team name, 30 characters at most, the same on all its rows.
courriel: the email address, optional, one per team. Without an email, you manage the team yourself.
joueur: the player's first and last name. Accents and capitals don't matter.
equipe_lnh: the NHL team, as an abbreviation (MTL) or the club name (Canadiens). It tells apart players with the same name. A team Estrade doesn't recognize gives a warning, not an error.
position: C, LW, RW, D or G. AG, AD, L, R, F and A are also read, and the cell can be left empty. EQ means an NHL team, if your lineup has a team slot: Estrade then reads the team in equipe_lnh.

No other columns: delete the rest. Save as CSV (commas, semicolons or tabs), or copy the table from the spreadsheet and paste it into Estrade.

The import in Estrade

In My pools, click Start a pool, choose Already-drafted pool and create the pool. You land on the import screen.
In Pool settings, copy the rules of your old pool: lineup, cap, scoring. The import screen opens again from the pool menu, Import a pool in progress.
Choose your file under CSV file, or paste your table under Or paste your table and click Read the table.
Under To fix, each problem gives its row: choose the right player, search for them, or click Remove the row. Nothing is saved while a problem remains.
Enter the points already earned, then click Import the pool. The Season Pass is paid before this step. Each pooler with an email in the file gets an invitation tied to their team. The import can't be undone.

A player missing from the NHL catalogue, like an AHL prospect, can't be imported: remove their row. The details of each screen are in the guide, under import a pool in progress.

Points already earned

Estrade doesn't recalculate the season: games count from the day of the import. On Marqueur, take each pooler's total from the TOT column of the Classement.

In a points pool, enter under Starting points each team's total, up to yesterday's games, with a Reason of 3 to 140 characters. Everyone sees it in the adjustment log.
In head-to-head, enter under Starting record each team's wins, losses and ties, up to the Sunday before the week of the import, with the same Reason. Points scored in earlier weeks are not carried over.

Entering it by hand

If nothing copies cleanly, start from the blank template that Download the template gives on the import screen. Type one row per player: the first and last name are enough. The NHL team and the position can stay empty; Estrade then asks you to choose between players with the same name.

The other platforms also have their page on moving a pool.