You need to join the two tables on the id column:
SELECT a.Id,a.Name, a.GP - p.GP AS DeltaGP, a.G - p.G AS DeltaG, a.A - p.A AS DeltaA
FROM dbo.table1 AS a --actual values
JOIN dbo.table2 AS p --predictions
ON a.Id = p.Id;
For an introduction to SQL Server Joins check out my post series here: http://sqlity.net/en/1146/a-join-a-day-introduction/
EDIT: If you have multiple rows per player in each table you need to aggregate them before you join:
SELECT a.Id,
a.Name,
a.GP - p.GP AS DeltaGP,
a.G - p.G AS DeltaG,
a.A - p.A AS DeltaA
FROM (
SELECT Id,
Name,
SUM(GP) AS GP,
SUM(G) AS G,
SUM(A) AS A
FROM dbo.table1
GROUP BY Id,
Name
) AS a --actual values
JOIN (
SELECT Id,
SUM(GP) AS GP,
SUM(G) AS G,
SUM(A) AS A
FROM dbo.table2
GROUP BY Id
) AS p
--predictions
ON a.Id = p.Id;
Depending on you requirements you might want to use AVG instead of SUM.