if you won´t to add a foreignkey to sf_guard_user put this on top off you schema.yml file ;)

propel:
  _attributes :          { package: "plugins.sfGuardPlugin.lib.model" }
  sf_guard_user:
    _attributes:         { phpName: sfGuardUser }
    id:

now you can simple add a foreignkey

propel:
  tbl_user_profile:
    user_id:             { type: integer, primaryKey: true, foreignTable: sf_guard_user, foreignReference: id, onDelete: cascade }

or

propel:
  tbl_user_profile:
    sf_guard_user_id:

if you using multiple database from Propel, It can be solve by writing two or more schema files.

PROJECT_DIR/config/databases.yml

all:
  database1:
    class:   sfPropelDatabase
    param:
      dsn:   pgsql://foo:bar@hostname/database1

  database2:
    class:   sfPropelDatabase
    param:
      dsn:   mysql://foo:bar@hostname/database2

PROJECT_DIR/config/database1.schema.xml

<?xml version="1.0" encoding="UTF-8"?>
<database name="database1" defaultIdMethod="native" noxsd="true">
　　<table name="foo" phpName="Foo">
    ....
　　</table>
</database>

PROJECT_DIR/config/database2.schema.xml

<?xml version="1.0" encoding="UTF-8"?>
<database name="database2" defaultIdMethod="native" noxsd="true">
　　<table name="bar" phpName="Bar">
    ....
　　</table>
</database>

Last, build model command.

$ symfony propel-build-model

Build complete.

Example, getting multiple databases connection handler.

$database1_connection_handler = Propel::getConnection(FooPeer::DATABASE_NAME);
$database2_connection_handler = Propel::getConnection(BarPeer::DATABASE_NAME);